NetNews Usenet Archive 1992 #19/NN_1992_19.iso/spool/comp/sources/misc/3878

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Newsgroups: comp.sources.misc
Path: sparky!kent
From: [e-mail] (Donald Tveter)
Subject:  v31i129:  backprop - Fast Backpropagation, Part01/04
Message-ID: <csm-v31i129=[e-mail]>
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Sender: [e-mail] (Kent Landfield)
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Date: Wed, 2 Sep 1992 18:06:40 GMT
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Submitted-by: [e-mail] (Donald Tveter)
Posting-number: Volume 31, Issue 129
Archive-name: backprop/part01
Supersedes: backprop: Volume 28, Issue 63-66
Environment: UNIX, DOS

   The programs described below were produced for my own use in studying
back-propagation and for doing some examples that are found in my
introduction to Artificial Intelligence textbook, The Basis of
Artificial Intelligence, to be published by Computer Science Press.  (I
hope some time before the sun burns out or before the Cubs win the World
Series or before Congress balances the budget or ...  .) I have
copyrighted these files but I hereby give permission to anyone to use
them for experimentation, educational purposes or to redistribute them
on a not for profit basis.  All others that want to use these programs
for business or commercial purposes I will charge you a small fee.  You
should contact me by mail at the address in the readme.

Changes/Additions vs. the February 1992 Version

   The programs now have the quickprop algorithm included with a few
experimental modifications of this algorithm as well.

Also I would be interested in hearing from anyone with suggestions,
bug reports and major successes or failures.  (Caution though:  email
in and out of the whole Chicago area is often unreliable.  Also from
time to time I get email and reply but the reply bounces.  If its
really important include a physical mail address.)

   There are four simulators that can be constructed from the included
files.  The program, rbp, does back-propagation using real weights and
arithmetic.  The program, bp, does back-propagation using 16-bit integer
weights, 16 and 32-bit integer arithmetic and some floating point
arithmetic.  The program, sbp, uses 16-bit integer symmetric weights but
only allows two-layer networks.  The program srbp does the same using
real weights.  The purpose of sbp and srbp is to produce networks that
can be used with the Boltzman machine relaxation algorithm (not
included).

   In general the 16-bit integer programs are the most useful because
they are the fastest.  Unfortunately, sometimes 16-bit integer weights
don't have enough range or precision and then using the floating point
versions may be necessary.  Many other speed-up techniques are included
in these programs.

See the file readme for more information.

Dr. Donald R. Tveter
5228 N. Nashville Ave.
Chicago, Illinois   60656
USENET:  [e-mail]
------
#! /bin/sh
# This is a shell archive.  Remove anything before this line, then unpack
# it by saving it into a file and typing "sh file".  To overwrite existing
# files, type "sh file -c".  You can also feed this as standard input via
# unshar, or by typing "sh <file", e.g..  If this archive is complete, you
# will see the following message at the end:
#        "End of archive 1 (of 4)."
# Contents:  readme
# Wrapped by drt@chinet on Mon Aug 24 08:57:28 1992
PATH=/bin:/usr/bin:/usr/ucb ; export PATH
if test -f 'readme' -a "${1}" != "-c" ; then
  echo shar: Will not clobber existing file \"'readme'\"
else
echo shar: Extracting \"'readme'\" \(46585 characters\)
sed "s/^X//" >'readme' <<'END_OF_FILE'
XFast Back-Propagation
XCopyright (c) 1990, 1991, 1992 by Donald R. Tveter
X
X
X1. Introduction
X
X   The programs described below were produced for my own use in studying
Xback-propagation and for doing some examples that are found in my
Xintroduction to Artificial Intelligence textbook, The Basis of
XArtificial Intelligence, to be published by Computer Science Press.  (I
Xhope some time before the sun burns out or before the Cubs win the World
XSeries or before Congress balances the budget or ...  .) I have
Xcopyrighted these files but I hereby give permission to anyone to use
Xthem for experimentation, educational purposes or to redistribute them
Xon a not for profit basis.  All others that want to use these programs
Xfor business or commercial purposes I will charge you a small fee.  You
Xshould contact me by mail at:
X
XDr. Donald R. Tveter
X5228 N. Nashville Ave.
XChicago, Illinois   60656
XUSENET:  [e-mail]
X
XAlso I would be interested in hearing from anyone with suggestions,
Xbug reports and major successes or failures.  (Caution though:  email
Xin and out of the whole Chicago area is often unreliable.  Also from
Xtime to time I get email and reply but the reply bounces.  If its
Xreally important include a physical mail address.)
X
X   Note:  this is use at your own risk software:  there is no guarantee
Xthat it is bug-free.  Use of this software constitutes acceptance for
Xuse in an as is condition.  There are no warranties with regard to this
Xsoftware. In no event shall the author be liable for any damages
Xwhatsoever arising out of or in connection with the use or performance
Xof this software.
X
X   There are four simulators that can be constructed from the included
Xfiles.  The program, rbp, does back-propagation using real weights and
Xarithmetic.  The program, bp, does back-propagation using 16-bit integer
Xweights, 16 and 32-bit integer arithmetic and some floating point
Xarithmetic.  The program, sbp, uses 16-bit integer symmetric weights but
Xonly allows two-layer networks.  The program srbp does the same using
Xreal weights.  The purpose of sbp and srbp is to produce networks that
Xcan be used with the Boltzman machine relaxation algorithm (not
Xincluded).
X
X   In general the 16-bit integer programs are the most useful because
Xthey are the fastest.  Unfortunately, sometimes 16-bit integer weights
Xdon't have enough range or precision and then using the floating point
Xversions may be necessary.  Many other speed-up techniques are included
Xin these programs.
X
XChanges/Additions vs. the February 1992 Version
X
X   The programs now have the quickprop algorithm included with a few
Xexperimental modifications of this algorithm as well.
X
X2. Making the Simulators
X
X   See the file, readme.mak.  (This file is getting too large for some
Xmailers.)
X
X3. A Simple Example
X
X  Each version would normally be called with the name of a file to read
Xcommands from, as in:
X
Xbp xor
X
XWhen no file name is specified bp will take commands from the keyboard
X(UNIX stdin file).  After the data file is read commands are then taken
Xfrom the keyboard.
X
X   The commands are one letter commands and most of them have optional
Xparameters.  The `A', `B', `d' and `f' commands allow a number of
Xsub-commands on a line.  The maximum length of any line is 256
Xcharacters.  An `*' is a comment and it can be used to make the
Xremainder of the line a comment.  Here is an example of a data file to
Xdo the xor problem:
X
X* input file for the xor problem
X
Xm 2 1 1           * make a 2-1-1 network
Xc 1 1 3 1         * add this extra connection
Xc 1 2 3 1         * add this extra connection
Xs 7               * seed the random number function
Xk 0 1             * give the network random weights
X
Xn 4               * read four new patterns into memory
X1 0 1
X0 0 0
X0 1 1
X1 1 0
X
Xe 0.5             * set eta to 0.5 (and eta2 to 0.5)
Xa 0.9             * set alpha to 0.9
X
XFirst in this example, the m command will make a network with 2 units
Xin the input layer, 1 unit in the second layer and 1 unit in the third
Xlayer.  The following c commands create extra connections from layer 1
Xunit 1 to layer 3 unit 1 and from layer 1 unit 2 to layer 3 unit 1.  The
X`s' command sets the seed for the random number function.  The `k'
Xcommand then gives the network random weights.  The `k' command has
Xanother use as well.  It can be used to try to kick a network out of a
Xlocal minimum.  Here, the meaning of "k 0 1" is to examine all the
Xweights in the network and for every weight equal to 0 (and they all
Xstart out at 0), add in a random number between -1 and +1.  The `n'
Xcommand specifies four new patterns to be read into memory.  With the
X`n' command, any old patterns that may have been present are removed.
XThere is also an `x' command that behaves like the `n' command, except
Xthe `x' commands ADDS the extra patterns to the current training
Xset.  The input pattern comes first followed by the output pattern.
XThe statement, e 0.5, sets eta, the learning rate for the upper layer to
X0.5 and eta2 for the lower layers to 0.5 as well.  The last line sets
Xalpha, the momentum parameter, to 0.9.
X
X   After these commands are executed the following messages and prompt
Xappears:
X
XFast Back-Propagation Copyright (c) 1990, 1991, 1992 by Donald R. Tveter
Xtaking commands from stdin now
X[?!*AaBbCcdefHhiklmnOoPpQqRrSstWwx]?
X
XThe characters within the square brackets are a list of the possible
Xcommands.  To run 100 iterations of back-propagation and print out the
Xstatus of the learning every 20 iterations type "r 100 20" at the
Xprompt:
X
X[?!*AaBbCcdefHhiklmnOoPpQqRrSstWwx]? r 100 20
X
XThis gives:
X
Xrunning . . .
X   20 iterations    0.00% right (0 right   4 wrong)   0.49927 error/unit
X   40 iterations    0.00% right (0 right   4 wrong)   0.43188 error/unit
X   60 iterations   75.00% right (3 right   1 wrong)   0.09033 error/unit
X   62 iterations  100.00% right (4 right   0 wrong)   0.07129 error/unit
Xpatterns learned to within 0.10 at iteration^G 62
X
XThe program immediately prints out the "running . . ." message.  After
Xeach 20 iterations a summary of the learning process is printed giving
Xthe percentage of patterns that are right, the number right and wrong
Xand the average value of the absolute values of the errors of the output
Xunits.  The program stops when the each output for each pattern has been
Xlearned to within the required tolerance, in this case the default value
Xof 0.1.  A ctrl-G is normally printed out as well to sound the bell.  If
Xthe second number defining how often to print out a summary is omitted
Xthe summaries will not be printed.  Sometimes the integer versions will
Xdo a few extra iterations before declaring the problem done because of
Xtruncation errors in the arithmetic done to check for convergence.  The
Xstatus figures for iteration i are computed when making the forward pass
Xof the iteration and before the weights are updated so these values are
Xone iteration out of date.  This saves on CPU time, however, if you
Xreally need up-do-date statistics use the u+ option described in the
Xformat specifications.
X
XListing Patterns
X
X   To get a listing of the status of each pattern use the `P' command
Xto give:
X
X[?!*AaBbCcdefHhiklmnOoPpQqRrSstWwx]? P
X  1  0.90  (0.098) ok
X  2  0.05  (0.052) ok
X  3  0.94  (0.062) ok
X  4  0.07  (0.074) ok
X   62 iterations  100.00% right (4 right   0 wrong)   0.07129 error/unit
X
XThe numbers in parentheses give the sum of the absolute values of the
Xoutput errors for each pattern.  An `ok' is given to every pattern that
Xhas been learned to within the required tolerance.  To get the status of
Xone pattern, say, the fourth pattern, type "P 4" to give:
X
X 0.07  (0.074) ok
X
XTo get a summary without the complete listing use "P 0".  To get the
Xoutput targets for a given pattern, say pattern 3, use "O 3".
X
X   A particular test pattern can be input to the network with the `p'
Xcommand, as in:
X
X[?!*AaBbCcdefHhiklmnOoPpQqRrSstWwx]? p 1 0
X 0.90
X
XExamining Weights
X
X   It is often interesting to see the values of some particular weights
Xin the network.  To see a listing of all the weights in a network use
Xthe save weights command described below and then cat the file weights,
Xhowever, to see the weights leading into a particular node, say the node
Xin row 2, node 1 use the w command as in:
X
X[?!*AaBbCcdefHhiklmnOoPpQqRrSstWwx]? w 2 1
Xlayer unit  unit value     weight         input from unit
X  1      1    1.00000     9.53516             9.53516
X  1      2    0.00000    -8.40332             0.00000
X  2      t    1.00000     4.13086             4.13086
X                                      sum =  13.66602
X
XThis listing also gives data on how the current activation value of the
Xnode is computed using the weights and the activations values of the
Xnodes feeding into unit 1 of layer 2.  The `t' unit is the threshold
Xunit.
X
XThe Help Command
X
X   To get a short description of any command, type `h' followed by the
Xletter of the command.  Here, we type h h for help with help:
X
X[?!*AaBbCcdefHhiklmnOoPpQqRrSstWwx]? h h
X
Xh <letter> gives help for command <letter>.
X
XTo list the status of all the parameters in the program, use `?'.
X
XTo Quit the Program
X
X   Finally, to end the program, the `q' (for quit) command is entered:
X
X[?!*AaBbCcdefHhiklmnOoPpQqRrSstWwx]? q
X
X
X4. The Format Command
X
X   There are several ways to input and output patterns, numbers and
Xother values and there is one format command, `f', that is used to set
Xthese options.  In the format command a number of options can be
Xspecified on a single line as for example in:
X
Xf b+ ir oc s- wB
X
XInput Patterns
X
X   The programs are able to read pattern values in two different
Xformats.  The default input format is the compressed format.  In it,
Xeach value is one character and it is not necessary to have blanks
Xbetween the characters.  For example, in compressed format the patterns
Xfor xor could be written out in either of the following ways:
X
X101      10 1
X000      00 0
X011      01 1
X110      11 0
X
XThe second example is preferable because it makes it easier to see the
Xinput and the output patterns.  Compressed format can also be used to
Xinput patterns with the `p' command.  In addition to using 1 and 0 as
Xinput the character, `?' can be used.  This character is initially
Xdefined to be 0.5, but it can be redefined using the Q command like so:
X
XQ -1
X
XThis sets the value of ?  to -1.  Other valid input characters are the
Xletters, `h', `i', `j' and `k'.  The `h' stands for `hidden'.  Its
Xmeaning in an input string is that the value at this point in the string
Xshould be taken from the next unit in the second layer of the network.
XThis notation is useful for specifying simple recurrent networks.
XNaturally, `i', `j' and `k' stand for taking input values from the
Xthird, fourth and fifth layers (if they exist).  A simple example of a
Xrecurrent network is given later.
X
X   The other input format for numbers is real.  The number portion must
Xstart with a digit (.35 is not allowed, but 0.35 is).  Exponential
Xnotation is not allowed.  Real numbers have to be separated by a space.
XThe `h', `i', `j', `k' and `?' characters are also allowed with real
Xinput patterns.  To take input in the real format it is necessary to
Xset the input format to be real using the `f' (format) command as in:
X
Xf ir
X
XTo change back to the compressed format use:
X
Xf ic
X
XOutput of Patterns
X
X   Output format is controlled with the `f' command as in:
X
Xf or
Xf oc
Xf oa
X
XThe first sets the output to real numbers.  The second sets the output
Xto be compressed mode where the value printed will be a `1' when the
Xunit value is greater than 1.0 - tolerance, a `^' when the value is
Xabove 0.5 but less than 1.0 - tolerance, a `v' when the value is less
Xthan 0.5 but greater than the tolerance.  Below the tolerance value a
X`0' is printed.  The tolerance can be changed using the `t' command (not
Xa part of the format command).  For example, to make all values greater
Xthan 0.8 print as `1' and all values less than 0.2 print as `0' use:
X
Xt 0.2
X
XOf course this same tolerance value is also used to check to see if all
Xthe patterns have converged.  The third output format is meant to give
X"analog compressed" output.  In this format a `c' is printed when a
Xvalue is close enough to its target value.  Otherwise, if the answer is
Xclose to 1, a `1' is printed, if the answer is close to 0, a `0' is
Xprinted, if the answer is above the target but not close to 1, a `^' is
Xprinted and if the answer is below the target but not close to 0, a `v'
Xis printed.  This output format is designed for problems where the
Xoutput is a real number, as for instance, when the problem is to make a
Xnetwork learn sin(x).
X
X   For the sake of convenience the output format (and only the output
Xformat) can be set without using the `f' so that:
X
Xor
X
Xwill also make the output format real.
X
XBreaking up the Output Values
X
X   In the compressed formats the default is to print a blank after
Xevery 10 values.  This can be altered using the `b' (for inserting
Xbreaks) command.  The use for this command is to separate output values
Xinto logical groups to make the output more readable.  For instance, you
Xmay have 24 output units where it makes sense to insert blanks after the
X4th, 7th and 19th positions.  To do this, specify:
X
Xb 4 7 19
X
XThen for example the output will look like:
X
X  1 10^0 10^ ^000v00000v0 01000 (0.17577)
X  2 1010 01v 0^0000v00000 ^1000 (0.16341)
X  3 0101 10^ 00^00v00000v 00001 (0.16887)
X  4 0100 0^0 000^00000v00 00^00 (0.19880)
X
XThe `b' command allows up to 20 break positions to be specified.  The
Xdefault output format is the real format with 10 numbers per line.  For
Xthe output of real values the `b' command specifies when to print a
Xcarriage return rather than when to print a blank.  (Note:  the `b'
Xcommand is not part of the `f' command.)
X
XPattern Formats
X
X   There are two different types of problems that back-propagation can
Xhandle, the general type of problem where every output unit can take on
Xan arbitrary value and the classification type of problem where the goal
Xis to turn on output unit i and turn off all the other output units when
Xthe pattern is of class i.  The xor problem is an example of the general
Xtype of problem.  For an example of a classification problem, suppose
Xyou have a number of data points scattered about through two-dimensional
Xspace and you have to classify the points as either class 1, class 2 or
Xclass 3.  For a pattern of class 1 you can always set up the output:
X"1 0 0", for class 2: "0 1 0" and for class 3: "0 0 1", however doing
Xthe translation to bit patterns can be annoying so another notation can
Xbe used.  Instead of specifying the bit patterns you can set the pattern
Xformat option to classification (as opposed to the default value of
Xgeneral) like so:
X
Xf pc
X
Xand then the program will read data in the form:
X
X   1.33   3.61   1   *  shorthand for 1 0 0
X   0.42  -2.30   2   *  shorthand for 0 1 0
X  -0.31   4.30   3   *  shorthand for 0 0 1
X
Xand translate it to the bit string form when the pattern is loaded onto
Xthe output units.  To switch to the general form use "f pg".
X
X   In addition to controlling the input of data the p command within
Xthe format command is used to control the output of patterns from a set
Xof test patterns kept on a file.  If the format is either c or g then
Xwhen the test set is run thru the network you will only get a summary of
Xhow many patterns are correct.  If the format is either C or G you will
Xget a listing of the output values for each pattern as well as the
Xsummary.  When reading patterns, C works the same as c and G works the
Xsame as g.
X
XControlling Summaries
X
X   When the program is learning patterns you can have it print out the
Xstatus of the learning process at regular intervals.  The default is to
Xprint out only a summary of how learning is going however you can also
Xprint out the status of every pattern at regular intervals.  To get the
Xwhole set of patterns use "f s-" to turn off the summary format and "f
Xs+" to go back to summarizing.
X
XRinging the Bell
X
X   To ring the bell when the learning has been completed use "f b+" and
Xto turn off the bell use "f b-".
X
XEchoing Input
X
X   When you are reading commands from a file it is often worthwhile to
Xsee those commands echoed on the screen.  To do this, use "f e+" and to
Xturn off the echoing, use "f e-".
X
XPaging
X
X   The program is set up to write 24 lines to the screen and then pause.
XAt the pause the program prints out a ":" (as does the UNIX System V
Xpager, pg).  At this point typing a carriage return will get you one
Xmore page.  Typing a "q" followed by a carriage return will quit the
Xprocess you're working on and give you another prompt.  So, if you're
Xrunning for example the xor problem and you type, "r 100 1" you will run
X24 iterations through the program, these will print out and then there
Xwill be a pause.  Notice that the program will not be busy computing
Xanything more during the pause.  To reset the number of lines written to
Xthe screen to say, 12, use "f P 12".  Setting the value to 0 will drop
Xthe paging altogether.
X
X   Note that the program will not be paging at all if you take a series
Xof commands from the original data file or some other input file and the
Xoutput produced by these commands is less than the page size.  That is
Xto say, a new line count is started every time a new command is read and
Xif the output of that command is less than the page size there won't be
Xany paging.
X
XMaking a Copy of Your Session
X
X   To make a copy of what appears on the screen use "f c+" to start
Xwriting to the file "copy" and "f c-" to stop writing to this file.
XEnding the session automatically closes this file as well.
X
XUp-To-Date Statistics
X
X   During the ith pass thru the network the program will collect
Xstatistics on how many patterns are correct and how much error there is
Xoverall.  These numbers are gathered before the weights are updated and
Xso the results listed for iteration i really show the situation after
Xthe weight update for iteration i-1.  To complicate matters more the
Xweight updates can be done continuously instead of after all the
Xpatterns have been presented so the statistics you get here are skewed
Xeven more.  If you want to have up-to-date statistics with either
Xmethod use "f u+" and to go back to statistics that are out of date
Xuse "f u-".  The penalty with "f u+" is that the program needs to do
Xanother forward pass.  When using the continuous update method it is
Xhighly advisable to use "f u+" at least when you get close to complete
Xconvergence because the default method of checking may claim the
Xlearning is finished when it isn't or it may continue training after the
Xtolerances have been met.
X
X 5. Taking Training and Testing Patterns from Files
X
X   In the xor example given above the four patterns were part of the
Xdata file and to read them in the following lines were used:
X
Xn 4
X1 0 1
X0 0 0
X0 1 1
X1 1 0
X
XHowever it is also convenient to take patterns from a file that
Xcontains nothing but a list of patterns (and possibly comments).  To
Xread a new set of patterns from some file, patterns, use:
X
Xn f patterns
X
XTo add an extra group of patterns to the current set you can use:
X
Xx f patterns
X
X   In addition to keeping a set of training patterns you can take
Xtesting patterns from a file as well.  To specify the file you can
Xinvoke the program with a second file name as in:
X
Xbp xor xtest
X
XIn addition, if you do the following:
X
Xt f xtest
X
Xthe program will set xtest as the test file and immediately do the
Xtesting.  Once the file has been defined you can test the patterns on
Xthe test file by "t f" or just "t".  (This leaves the t command doing
Xdouble duty since "t <real>" will set the tolerance to <real>.) Also in
Xaddition, the test file can be set without being tested by using
X
XB t f xtest
X
Xas explained in the benchmarking section.
X
X
X6. Saving and Restoring Weights and Related Values
X
X   Sometimes the amount of time and effort needed to produce a set of
Xweights to solve a problem is so great that it is more convenient to
Xsave the weights rather than constantly recalculate them.  Weights can
Xbe saved as real values in an ASCII format (the default) or as binary
Xto save space.  The old way to save the weights (which still works) is
Xto enter the command, "S".  The weights are then written on a file
Xcalled "weights" or to the last file name you have specified, if you're
Xusing the new version of the command.  The following file comes from the
Xxor problem:
X
X62r   file = ../xor3
X    9.5351562500
X   -8.4033203125
X    4.1308593750
X    5.5800781250
X   -4.9755859375
X  -11.3095703125
X    8.0527343750
X
XTo write the weights the program starts with the second layer, writes
Xout the weights leading into these units in order with the threshold
Xweight last, then it moves on to the third layer, and so on.  To
Xrestore these weights type an `R' for restore.  At this time the
Xprogram reads the header line and sets the total number of iterations
Xthe program has gone through to be the first number it finds on the
Xheader line.  It then reads the character immediately after the number.
XThe `r' indicates that the weights will be real numbers represented as
Xcharacter strings.  If the weights were binary the character would be a
X`b' rather than an `r'.  Also, if the character is `b', the next
Xcharacter is read.  This next character indicates how many bytes are
Xused per value.  The integer versions bp and sbp write files with 2
Xbytes per weight while the real versions rbp and srbp write files with
X8 bytes per weight for double precision reals and 4 bytes per weight for
Xsingle precision reals.  With this notation weight files written by one
Xprogram can be read by the other.  A binary weight format is specified
Xwithin the `f' command by using "f wb".  A real format is specified by
Xusing "f wr".  If your program specifies that weights should be written
Xin one format but the weight file you read from is different a notice
Xwill be given.  There is no check made to see if the number of weights
Xon the file equals the number of weights in the network.
X
X   The above formats specify that only weights are written out and this
Xis all you need once the patterns have converged.  However, if you're
Xstill training the network and want to break off training and pick up
Xthe training from exactly the same point later on you need to save the
Xold weight changes when using momentum and the parameters for the
Xdelta-bar-delta method if you are using this technique.  To save these
Xextra parameters on the weights file use "f wR" to write the extra
Xvalues as real and "f wB" to write the extra values as binary.
X
X   In the above example the command, S, was used to save the weights
Ximmediately.  Another alternative is to save weights at regular
Xintervals.  The command, S 100, will automatically save weights every
X100 iterations the program does.  The default rate at which to save
Xweights is set at 32767 for 16-bit compilers and 2147483647 for 32-bit
Xcompilers which generally means that no weights will ever be saved.
X
X   To save weights to a file other than "weights" you can say:
X"s w <filename>", where, of course, <filename> is the file you want to
Xsave to.  To continue saving to the same file you can just do "s w".
XNaturally if you restore weights it will be from this current weights
Xfile as well.  You can restore weights from another file by using:
X"r w <filename>".  Of course this also sets the name of the file to
Xwrite to so if you're not careful you could lose your original weights
Xfile.
X
X7. Initializing Weights and Giving the Network a `Kick'
X
X   All the weights in the network initially start out at 0.  In
Xsymmetric networks then no learning may result because error signals
Xcancel themselves out.  Even in non-symmetric networks the training
Xprocess will usually converge faster if the weights start out at small
Xrandom values.  To do this the `k' command will take the network and
Xalter the weights in the following ways.  Suppose the command given is:
X
Xk 0 0.5
X
XNow if a weight is exactly 0, then the weight will be changed to a
Xrandom value between +0.5 and -0.5.  The above command can therefore be
Xused to initialize the weights in the network.  A more complex use of
Xthe `k' command is to decrease the magnitude of large weights in the
Xnetwork by a certain random amount.  For instance in the following
Xcommand:
X
Xk 2 8
X
Xall the weights in the network that are greater than or equal to 2 will
Xbe decreased by a random number between 0 and 8.  Weights less than or
Xequal to -2 will be increased by a random number between 0 and 8.  The
Xseed to the random number generator can be changed using the `s' command
Xas in "s 7".  The integer parameter in the `s' command is of type,
Xunsigned.
X
X   Another method of giving a network a kick is to add hidden layer
Xunits.  The command:
X
XH 2 0.5
X
Xadds one unit to layer 2 of the network and all the weights that are
Xcreated are initialized to between - 0.5 and + 0.5.
X
X   The subject of kicking a back-propagation network out of local minima
Xhas barely been studied and there is no guarantee that the above methods
Xare very useful in general.
X
X8. Setting the Algorithm to Use
X
X   A number of different variations on the original back-propagation
Xalgorithm have been proposed in order to speed up convergence and some
Xof these have been built into these simulators.  These options are set
Xusing the `A' command and a number of options can go on the one line.
X
XActivation Functions
X
X   To set the activation function use:
X
XA al * for the linear activation function
XA ap * for the piece-wise activation function
XA as * for the smooth activation function
XA at * for the piecewise near-tanh function that runs from -1 to +1
XA aT * for the continuous near-tanh function that runs from -1 to +1
X
XWhen using the linear activation function it is only appropriate to use
Xthe differential step-size derivative and a two-layer network.  The
Xsmooth activation function is:
X
Xf = 1.0 / (1.0 + exp(-x))
X
Xwhere x is the input to a unit.  The piece-wise function is an
Xapproximation to the function, f and it will normally save some CPU
Xtime even though it may increase the number of iterations you need to
Xsolve the problem.  The continuous near-tanh function is 2f - 1 and the
Xpiece-wise version approximates this function with a series of straight
Xlines.
X
XSharpness (or Gain)
X
X   The sharpness (or gain) is the parameter, D, in the function:
X
X1.0 / (1.0 + exp(-D*x)).
X
XA sharper sigmoid shaped activation function (larger D) will produce
Xfaster convergence (see "Speeding Up Back Propagation" by Yoshio Izui
Xand Alex Pentland in the Proceedings of IJCNN-90-WASH-DC, Lawrence
XErlbaum Associates, 1990).  To set this parameter to say, 8, use
X"A D 8".  The default value is 1.  Unfortunately, too large a value
Xfor D will hurt convergence so this is not a perfect solution to
Xspeeding up learning.  Sometimes the best value for D may be less than
X1.0.  A larger D is also useful in the integer version of
Xback-propagation where the weights are limited to between -32 and
X+31.999.  A larger D value in effect magnifies the weights and makes it
Xpossible for the weights to stay smaller.  Values of D less than one may
Xbe useful in extracting a network from a local minima (see "Handwritten
XNumeral Recognition by Multi-layered Neural Network with Improved
XLearning Algorithm" by Yamada, Kami, Temma and Tsukumo in Proceedings of
Xthe 1989 IJCNN, IEEE Press).  A smaller value of D will also force the
Xweights and the weight changes to be larger and this may be of value
Xwhen the weight changes become less than the weight resolution of 0.001
Xin the integer version.
X
XThe Derivatives
X
X   The correct derivative for the standard activation function is s(1-s)
Xwhere s is the activation value of a unit however when s is near 0 or 1
Xthis term will give only very small weight changes during the learning
Xprocess.  To counter this problem Fahlman proposed the following one
Xfor the output layer:
X
X0.1 + s(1-s)
X
X(For the original description of this method see "Faster Learning
XVariations of Back-Propagation:  An Empirical Study", by Scott E.
XFahlman, in Proceedings of the 1988 Connectionist Models Summer School,
XMorgan Kaufmann, 1989.)  Besides Fahlman's derivative and the original
Xone the differential step size method (see "Stepsize Variation Methods
Xfor Accelerating the Back-Propagation Algorithm", by Chen and Mars, in
XIJCNN-90-WASH-DC, Lawrence Erlbaum, 1990) takes the derivative to be 1
Xin the layer going into the output units and uses the correct derivative
Xterm for all other layers.  The learning rate for the inner layers is
Xnormally set to some smaller value.  To set a value for eta2 give two
Xvalues in the `e' command as in:
X
Xe 0.1 0.01
X
XTo set the derivative use the `A' command as in:
X
XA dd   * use the differential step size derivative (default)
XA dF   * use Fahlman's derivative in only the output layer
XA df   * use Fahlman's derivative in all layers
XA do   * use the original, correct derivative
X
XUpdate Methods
X
X   The choices are the periodic (batch) method, the continuous (online)
Xmethod, delta-bar-delta and quickprop.  The following commands set the
Xupdate methods:
X
XA uc   * for the continuous update method
XA ud   * for the delta-bar-delta method
XA up   * for the original periodic update method (default)
XA uq   * for the quickprop algorithm
X
XThe delta-bar-delta method uses a number of special parameters and these
Xare set using the `d' command.  Delta-bar-delta can be used with any of
Xthe derivatives and the algorithm will find its own value of eta for
Xeach weight.
X
XOther Algorithm Options
X
X   The `b' command controls whether or not to backpropagate error for
Xunits that have learned their response to within a given tolerance.  The
Xdefault is to always backpropagate error.  The advantage to not
Xbackpropagating error is that this can save computer time.  This
Xparameter can be set like so:
X
XA b+   * always backpropagate error
XA b-   * don't backpropagate error when close
X
X   The `s' sub-command will set the number of times to skip a pattern
Xwhen the pattern has been learned to within the desired tolerance.  To
Xskip 3 iterations, use "A s 3", to reset to not skip any patterns
Xuse "A s 0".
X
X   The `t' sub-command will take the given pattern (only one at a
Xtime) out of the training set so that you can then train the other
Xpatterns and test the network's response to this one pattern that was
Xremoved.  To test pattern 3 use "A t 3" and to reset to use all the
Xpatterns use "A t 0".
X
X
X9. The Delta-Bar-Delta Method
X
X   The delta-bar-delta method attempts to find a learning rate, eta, for
Xeach individual weight.  The parameters are the initial value for the
Xetas, the amount by which to increase an eta that seems to be too small,
Xthe rate at which to decrease an eta that is too large, a maximum value
Xfor each eta and a parameter used in keeping a running average of the
Xslopes.  Here are examples of setting these parameters:
X
Xd d 0.5    * sets the decay rate to 0.5
Xd e 0.1    * sets the initial etas to 0.1
Xd k 0.25   * sets the amount to increase etas by (kappa) to 0.25
Xd m 10     * sets the maximum eta to 10
Xd n 0.005  * an experimental noise parameter
Xd t 0.7    * sets the history parameter, theta, to 0.7
X
XThese settings can all be placed on one line:
X
Xd d 0.5  e 0.1  k 0.25  m 10  t 0.7
X
XThe version implemented here does not use momentum.  The symmetric
Xversions sbp and srbp do not implement delta-bar-delta.
X
X   The idea behind the delta-bar-delta method is to let the program find
Xits own learning rate for each weight.  The `e' sub-command sets the
Xinitial value for each of these learning rates.  When the program sees
Xthat the slope of the error surface averages out to be in the same
Xdirection for several iterations for a particular weight the program
Xincreases the eta value by an amount, kappa, given by the `k' parameter.
XThe network will then move down this slope faster.  When the program
Xfinds the slope changes signs the assumption is that the program has
Xstepped over to the other side of the minimum and so it cuts down the
Xlearning rate by the decay factor given by the `d' parameter.  For
Xinstance, a d value of 0.5 cuts the learning rate for the weight in
Xhalf.  The `m' parameter specifies the maximum allowable value for an
Xeta.  The `t' parameter (theta) is used to compute a running average of
Xthe slope of the weight and must be in the range 0 <= t < 1.  The
Xrunning average at iteration i, a[i], is defined as:
X
Xa[i] = (1 - t) * slope[i] + t * a[i-1],
X
Xso small values for t make the most recent slope more important than the
Xprevious average of the slope.  Determining the learning rate for
Xback-propagation automatically is, of course, very desirable and this
Xmethod often speeds up convergence by quite a lot.  Unfortunately, bad
Xchoices for the delta-bar-delta parameters give bad results and a lot of
Xexperimentation may be necessary.  If you have n patterns in the
Xtraining set try starting e and k around 1/n.  The n parameter is an
Xexperimental noise term that is only used in the integer version.  It
Xchanges a weight in the wrong direction by the amount indicated when the
Xprevious weight change was 0 and the new weight change would be 0 and
Xthe slope is non-zero.  (I found this to be effective in an integer
Xversion of quickprop so I tossed it into delta-bar-delta as well.  If
Xyou find this helps please let me know.)  For more on delta-bar-delta
Xsee "Increased Rates of Convergence" by Robert A. Jacobs, in Neural
XNetworks, Volume 1, Number 4, 1988.
X
X10. Quickprop
X
X    Quickprop (see "Faster-Learning Variations on Back-Propagation: An
XEmpirical Study", by Scott E. Fahlman, in Proceedings of the 1988
XConnectionist Models Summer School", Morgan Kaufmann, 1989.) is similar
Xto delta-bar-delta in that the algorithm attempts to increase the size
Xof a weight change for each weight while the process continues to go
Xdownhill in terms of error.  The main acceleration technique is to make
Xthe next weight change mu times the previous weight change.  Fahlman
Xsuggests mu = 1.75 is generally quite good so this is the initial value
Xfor mu but slightly larger or slightly smaller values are sometimes
Xbetter.  In addition when this is done Fahlman also adds in a value,
Xeta times the current slope, in the traditional backprop fashion.  I had
Xto wonder if this was a good idea so in this code I've included a
Xcapability to add it in or not add it in.  So far it seems to me that
Xsometimes adding in this extra term helps and sometimes it doesn't.  The
Xdefault is to always use the extra term.
X
X   A second key property of quickprop is that when a weight change
Xchanges the slope of the error curve from positive to negative or
Xvice-versa, quickprop attempts to jump to the minimum by assuming the
Xcurve is a parabola.
X
X   A third factor involved in quickprop comes about from the fact that
Xthe weights often grow very large very quickly.  To minimize this
Xproblem there is a decay factor designed to keep the weights small.
XFahlman does not mention a value for this parameter but I usually try
X0.0001 to 0.00001.  I've found that too large a decay factor can stall
Xout the learning process so that if your network isn't learning fast
Xenough or isn't learning at all one possible fix is to decrease the
Xdecay factor.  The small values you need present a problem for the
Xinteger version since the smallest value you can represent is about
X0.001.  To get around this problem the decay value you input should be
X1000 times larger than the value you intend to use.  So to get 0.0001,
Xinput 0.1, to get 0.00001, input 0.01, etc.  The code has been written
Xso that the factor of 1000 is taken into account during the calculations
Xinvolving the decay factor.  To keep the values consistent both the
Xinteger and floating point versions use this convention.  If you use
Xquickprop elsewhere you need to take this factor of 1000 into account.
XThe default value for the decay factor is 0.1 (=0.0001).
X
X   I built in one additional feature for the integer version.  I found
Xthat by adding small amounts of noise the time to convergence can be
Xbrought down and the number of failures can be decreased somewhat.  This
Xseems to be especially true when the weight changes get very small.  The
Xnoise consists of moving uphill in terms of error by a small amount when
Xthe previous weight change was zero.  Good values for the noise seem to
Xbe around 0.005.
X
X   The parameters for quickprop are all set in the `qp' command like
Xso:
X
Xqp d 0.1  * the default decay factor
Xqp e 0.5  * the default value for eta
Xqp m 1.75 * the default value for mu
Xqp n 0    * the default value for noise
Xqp s+     * always include the slope
X
Xor a whole series can go on one line:
X
Xqp d 0.1 e 0.5 m 1.75 n 0 s+
X
X
X11. Recurrent Networks
X
X   Recurrent back-propagation networks take values from higher level
Xunits and use them as activation values for lower level units.  This
Xgives a network a simple kind of short-term memory, possibly a little
Xlike human short-term memory.  For instance, suppose you want a network
Xto memorize the two short sequences, "acb" and "bcd".  In the middle of
Xboth of these sequences is the letter, "c".  In the first case you want
Xa network to take in "a" and output "c", then take in "c" and output
X"b".  In the second case you want a network to take in "b" and output
X"c", then take in "c" and output "d".  To do this a network needs a
Xsimple memory of what came before the "c".
X
X   Let the network be an 7-3-4 network where input units 1-4 and output
Xunits 1-4 stand for the letters a-d.  Furthermore, let there be 3 hidden
Xlayer units.  The hidden units will feed their values back down to the
Xinput units 5-7 where they become input for the next step.  To see why
Xthis works, suppose the patterns have been learned by the network.
XInputting the "a" from the first string produces some random pattern of
Xactivation, p1, on the hidden layer units and "c" on the output units.
XThe pattern p1 is copied down to units 5-7 of the input layer.  Second,
Xthe letter, "c" is presented to the network together with p1 now on
Xunits 5-7.  This will give "b" on the output units.  However, if the "b"
Xfrom the second string is presented first there will be a different
Xrandom pattern, p2, on the hidden layer units.  These values are copied
Xdown to input units 5-7.  These values combine with the "c" to produce
Xthe output, "d".
X
X   The training patterns for the network can be:
X
X     1000 000   0010  * "a" prompts the output, "c"
X     0010 hhh   0100  * inputting "c" should produce "b"
X
X     0100 000   0010  * "b" prompts the output, "c"
X     0010 hhh   0001  * inputting "c" should produce "d"
X
Xwhere the first four values on each line are the normal input, the
Xmiddle three either start out all zeros or take their values from the
Xprevious values of the hidden units.  The code for taking these values
Xfrom the hidden layer units is "h".  The last set of values represents
Xthe output that should be produced.  To take values from the third layer
Xof a network, the code is "i".  For the fourth and fifth layers (if they
Xexist) the codes are "j" and "k".  Training recurrent networks can take
Xmuch longer than training standard networks and the average error can
Xjump up and down quite a lot.
X
X
X12. The Benchmarking Command
X
X   The main purpose of the benchmarking command is to make it possible
Xto run a number of tests of a problem with different initial weights and
Xaverage the number of iterations and CPU time for networks that
Xconverged.  A second purpose is to run a training set thru the network a
Xnumber of times and for each try a test pattern or a test set can be
Xchecked at regular intervals.
X
X   A typical command to simply test the current parameters on a number
Xof networks is:
X
XB g 5 m 15 k 1 r 1000 200
X
XThe "g 5" specifies that you'd like to set the goal of getting 5
Xnetworks to converge but the "m 15" sets a maximum of 15 tries to
Xreach this goal.  The k specifies that each initial network will get
Xa kick by setting each weight to a random number between -1 and 1.
XThe "r 1000 200" portion specifies that you should run up to 1000
Xiterations on a network and print the status of learning every 200
Xiterations.  This follows the normal run command and the second
Xparameter defining how often to print the statistics can be omitted.
XFor example, here is some output from benchmarking with the xor problem:
X
X[?!*AaBbCcdefHhiklmnOoPpQqRrSstWwx]? B g 5 m 5 k 1 r 200
X seed =      7; running . . .
Xpatterns learned to within 0.10 at iteration 62
X seed =      7; running . . .
X seed =      7; running . . .
Xpatterns learned to within 0.10 at iteration 54
X seed =      7; running . . .
Xpatterns learned to within 0.10 at iteration 39
X seed =      7; running . . .
Xpatterns learned to within 0.10 at iteration 44
X1 failures; 4 successes; average = 49.750000     0.333320 sec/network
X
XThe time/network includes however much time is used to print messages so
Xto time the process effectively all printing should be minimized.  When
Xthe timing is done on a UNIX PC the time returned by clock will overflow
Xafter 2147 seconds or about 36 minutes.  If you system has the same
Xlimitation take care that ALL of the benchmarking you do in a single
Xcall of the program adds up to less than 36 minutes.
X
X   In the above example the seed that was used to set the random values
Xfor the weights was set to 7 (outside the benchmarking command) however
Xif you set a number of seeds as in:
X
Xs 3 5 7 18484 99
X
Xthe seeds will be taken in order for each network.  When there are more
Xnetworks to try than there are seeds the random values keep coming from
Xthe last seed value so actually you can get by using a single seed.
XThe idea behind allowing multiple seeds is so that if one network does
Xsomething interesting you can use that seed to run a network with the
Xsame initial weights outside of the benchmarking command.
X
X   Once the benchmarking parameters have been set it is only necessary
Xto include the run portion in order to start the benchmarking process
Xagain, thus, "B r 200" will run benchmarking again using the current set
Xof parameters.  Also, the parameters can be set without starting the
Xbenchmarking process by just not including the `r' parameters in the B
Xcommand as in:
X
XB g 5 m 5 k 1
X
X   In addition to getting data on convergence you can have the program
Xrun test patterns thru the network at the print statistics rate given
Xin the `r' sub-command.  To specify the test file, test100, use:
X
XB t f test100
X
XTo run the training data thru for up to 1000 iterations and test every
X200 iterations use:
X
XB r 1000 200
X
XIf the pattern format specification p is set to either c or g you will
Xget a summary of the patterns on the test file.  If p is either C or G
Xyou will get the results for each pattern listed as well as the summary.
XTo stop testing the data on the data file use "B t 0".
X
X   Sometimes you may have so little data available that it is difficult
Xto separate the patterns into a training set and a test set.  One
Xsolution is to remove each pattern from the training set, train the
Xnetwork on the remaining patterns and then test the network on the
Xpattern that was removed.  To remove a pattern, say pattern 1 from the
Xtraining set use:
X
XB t 1
X
XTo systematically remove each pattern from the training set use a data
Xfile with the following commands:
X
XB t 1 r 200 50
XB t 2 r 200 50
XB t 3 r 200 50
X ... etc.
X
Xand the pattern will be tested every 50 iterations.  If, in the course
Xof training the network, all the patterns converge, the program will
Xprint out a line starting with a capital S followed by a test of the
Xtest pattern.  If the programs hits the point where statistics on the
Xlearning process have to be printed and the network has not converged
Xthen a capital F will print out followed by a test of the test pattern.
XTo stop this testing use "B t 0".
X
X   It would be nice to have the program average up and tabulate all the
Xdata that comes out of the benchmarking command but I thought I'd leave
Xthat to users for now.  You can use the record command to save the
Xoutput from the entire session and then run it thru some other program,
Xsuch as an awk program in order to sort everything out.
X
X
X13. Miscellaneous Commands
X
X   Below is a list of some miscellaneous commands, a short example of
Xeach and a short description of the command.
X
X
X!   Example: ! ls
X
XAnything after `!' will be passed on to the OS as a command to execute.
X
X
XC   Example: C
X
XThe C command will clear the network of values, reset the number of
Xiterations to 0 and reset other values so that another run can be made.
XThe seed value is reset so you can run the same network over with the
Xsame initial weights but with different learning parameters.  Even
Xthough the seed is reset the weights are not initialized so you
Xmust do this step after clearing the network.
X
X
Xi   Example: i f
X
XEntering "i f" will read commands from the file, f.  When there are no
Xmore commands on the file the program resumes reading from the previous
Xfile being used.  You can also have an `i' command within the file f,
Xhowever the depth to which you can nest the number of active files is 4
Xand stdin itself counts as the first one.  Once an input file has been
Xspecified you can simply type "i" to read from the file again.
X
X
Xl   Example: l 2
X
XEntering "l 2" will print the values of the units on layer 2, or
Xwhatever layer is specified.
X
X
XT   Example: T -3
X
XIn sbp and srbp only, "T -3" sets all the threshold weights to -3 or
Xwhatever value is specified and freezes them at this value.
X
X
XW   Example: W 0.9
X
XEntering "W 0.9" will remove (whittle away) all the weights with
Xabsolute values less than 0.9.
X
XIn addition, under UNIX when a user generated interrupt occurs (by
Xtyping DEL) the program will drop its current task and take the next
Xcommand from the keyboard.  Under DOS you can use ctrl-C to stop the
Xcurrent task and take the next command from the keyboard.  Also under
XDOS, when the program is executing a run command hitting the escape key
Xwill get the program to stop after the current iteration.
X
X
X13. Limitations
X
X   Weights in the bp and sbp programs are 16-bit integer weights where
Xthe real value of the weight has been multiplied by 1024.  The integer
Xversions cannot handle weights less than -32 or greater than 31.999.
XThe weight changes are all checked for overflow but there are other
Xplaces in these programs where calculations can possibly overflow as
Xwell and none of these places are checked.  Input values for the integer
Xversions can run from -31.994 to 31.999.  Due to the method used to
Ximplement recurrent connections, input values in the real version are
Xlimited to -31994.0 and above.
END_OF_FILE
if test 46585 -ne `wc -c <'readme'`; then
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# end of 'readme'
fi
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##  End of shell archive.
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exit 0 # Just in case...