Libris Britannia 4/science library(b).zip/science library(b)/MATHEMAT/0302.ZIP/HELP

Text File | 1986-02-06 | 34KB | 757 lines

HELP is available

NEWS  MATLAB NEWS dated 9/15/83.
      HELP is now a lot faster.

INTRO Welcome to MATLAB.

      Here are a few sample statements:

      A = <1 2; 3 4>
      b = <5 6>'
      x = A\b
      <V,D> = eig(A),  norm(A-V*D/V)
      help \ , help eig
      exec('demo',7)

      For more information, see the MATLAB Users' Guide which  is
      contained in file ...  or may be obtained from ... .

<     < > Brackets used in forming vectors and matrices.
      <6.9  9.64  SQRT(-1)>  is  a  vector  with  three  elements
      separated  by  blanks.   <6.9,  9.64, sqrt(-1)> is the same
      thing.  <1+I 2-I 3>  and  <1 +I 2 -I 3>  are not the  same.
      The first has three elements, the second has five.
      <11 12 13; 21 22 23>  is a 2 by 3 matrix .   The  semicolon
      ends the first row.

      Vectors and matrices can be used inside < > brackets.
      <A B; C>  is allowed if the number of rows  of   A   equals
      the  number  of rows of  B  and the number of columns of  A
      plus the number of columns of   B   equals  the  number  of
      columns  of   C  .   This  rule  generalizes in a hopefully
      obvious way to allow fairly complicated constructions.

      A = < >  stores an empty matrix in  A , thereby removing it
      from the list of current variables.

      For the use of < and > on the left of  the  =  in  multiple
      assignment statements, see LU, EIG, SVD and so on.

      In WHILE and IF clauses, <>  means  less  than  or  greater
      than,  i.e.  not  equal, < means less than, > means greater
      than, <= means less than or equal, >= means greater than or
      equal.

      For the use of > and < to delineate macros, see MACRO.

>     See < .  Also see MACRO.

(     ( ) Used to indicate precedence in  arithmetic  expressions
      in  the  usual way.  Used to enclose arguments of functions
      in the usual way.  Used to enclose  subscripts  of  vectors
      and  matrices  in  a  manner somewhat more general than the
      usual way.  If  X   and   V  are  vectors,  then   X(V)  is
      <X(V(1)),  X(V(2)),  ...,  X(V(N))> .  The components of  V
      are rounded to nearest integers and used as subscripts.  An
      error  occurs  if  any  such  subscript  is  less than 1 or
      greater than the dimension of  X .  Some examples:
      X(3)  is the third element of  X .
      X(<1 2 3>)  is the first three elements of  X .  So is
      X(<SQRT(2), SQRT(3), 4*ATAN(1)>)  .
      If  X  has  N  components,  X(N:-1:1) reverses them.
      The same indirect subscripting is used in matrices.  If   V
      has   M  components and  W  has  N  components, then A(V,W)
      is the  M by N  matrix formed from the elements of A  whose
      subscripts are the elements of  V  and  W .  For example...
      A(<1,5>,:) = A(<5,1>,:)  interchanges rows 1 and 5 of  A .

)     See  ( .

=     Used in assignment statements and to mean equality in WHILE
      and IF clauses.

.     Decimal point.  314/100, 3.14  and   .314E1   are  all  the
      same.

      Element-by-element multiplicative operations  are  obtained
      using  .*  ,  ./  , or .\ .  For example, C = A ./ B is the
      matrix with elements  c(i,j) = a(i,j)/b(i,j) .

      Kronecker tensor products and quotients are  obtained  with
      .*. , ./.  and .\. .  See KRON.

      Two or  more  points  at  the  end  of  the  line  indicate
      continuation.    The   total  line  length  limit  is  1024
      characters.

,     Used to separate matrix subscripts and function  arguments.
      Used  at  the  end  of  FOR, WHILE and IF clauses.  Used to
      separate statements  in  multi-statement  lines.   In  this
      situation,  it  may  be  replaced  by semicolon to suppress
      printing.

;     Used inside brackets to end rows.
      Used after an expression or statement to suppress printing.
      See SEMI.

\     Backslash or matrix left division.   A\B   is  roughly  the
      same  as   INV(A)*B  , except it is computed in a different
      way.  If  A  is an N by N matrix and  B  is a column vector
      with  N  components, or a matrix with several such columns,
      then X = A\B  is the solution to  the  equation   A*X  =  B
      computed  by  Gaussian  elimination.   A warning message is
      printed if  A is badly scaled or nearly singular.
      A\EYE produces the inverse of  A .

      If  A  is an  M by N  matrix with  M < or > N  and  B  is a
      column vector with  M  components, or a matrix with several
      such columns, then  X = A\B  is the solution in  the  least
      squares  sense  to  the under- or overdetermined system  of
      equations A*X = B .  The  effective  rank,  K,  of   A   is
      determined  from  the  QR  decomposition  with pivoting.  A
      solution  X  is  computed  which  has  at  most  K  nonzero
      components  per column.  If  K < N this will usually not be
      the same solution as PINV(A)*B .
      A\EYE produces a generalized inverse of  A .

      If A and B have the  same  dimensions,  then  A  .\  B  has
      elements a(i,j)\b(i,j) .

      Also, see EDIT.

/     Slash or matrix right division.  B/A  is roughly  the  same
      as  B*INV(A) .  More precisely,  B/A = (A'\B')' .  See \ .

      IF A and B have the  same  dimensions,  then  A  ./  B  has
      elements a(i,j)/b(i,j) .

      Two or more slashes together on a line indicate  a  logical
      end of line.  Any following text is ignored.

'     Transpose.  X'  is the complex conjugate transpose of  X  .
      Quote.   'ANY  TEXT'   is a vector whose components are the
      MATLAB internal codes for the characters.  A  quote  within
      the text is indicated by two quotes.  See DISP and FILE .

+     Addition.  X + Y .  X and Y must have the same dimensions.

-     Subtraction.  X  -  Y  .   X  and  Y  must  have  the  same
      dimensions.

*     Matrix multiplication, X*Y .  Any scalar (1  by  1  matrix)
      may multiply anything.  Otherwise, the number of columns of
      X must equal the number of rows of Y .

      Element-by-element multiplication is obtained with X .* Y .

      The Kronecker tensor product is denoted by X .*. Y .

      Powers.  X**p  is  X  to the   p   power.   p   must  be  a
      scalar.  If  X  is a matrix, see  FUN .

:     Colon.  Used in subscripts,  FOR  iterations  and  possibly
      elsewhere.
      J:K  is the same as  <J, J+1, ..., K>
      J:K  is empty if  J > K .
      J:I:K  is the same as  <J, J+I, J+2I, ..., K>
      J:I:K  is empty if  I > 0 and J > K or if I < 0 and J < K .
      The colon notation can be used to pick out  selected  rows,
      columns and elements of vectors and matrices.
      A(:)  is all the  elements  of  A,  regarded  as  a  single
      column.
      A(:,J)  is the  J-th  column of A
      A(J:K)  is  A(J),A(J+1),...,A(K)
      A(:,J:K)  is  A(:,J),A(:,J+1),...,A(:,K) and so on.
      For the use of the colon in the FOR statement, See FOR .

ABS   ABS(X)  is the absolute value, or complex modulus,  of  the
      elements of X .

ANS   Variable created automatically  when  expressions  are  not
      assigned to anything else.

ATAN  ATAN(X)  is the arctangent of  X .  See FUN .

BASE  BASE(X,B) is a vector containing the base B  representation
      of   X  .   This is often used in conjunction with DISPLAY.
      DISPLAY(X,B)  is  the  same  as  DISPLAY(BASE(X,B)).    For
      example,    DISP(4*ATAN(1),16)   prints   the   hexadecimal
      representation of pi.

CHAR  CHAR(K)  requests  an  input  line  containing   a   single
      character  to  replace  MATLAB  character  number  K in the
      following table.  For example, CHAR(45) replaces backslash.
      CHAR(-K) replaces the alternate character number K.

                K  character alternate name
              0 - 9   0 - 9    0 - 9   digits
             10 - 35  A - Z    a - z   letters
               36                      blank
               37       (        (     lparen
               38       )        )     rparen
               39       ;        ;     semi
               40       :        |     colon
               41       +        +     plus
               42       -        -     minus
               43       *        *     star
               44       /        /     slash
               45       \        $     backslash
               46       =        =     equal
               47       .        .     dot
               48       ,        ,     comma
               49       '        "     quote
               50       <        [     less
               51       >        ]     great

CHOL  Cholesky factorization.  CHOL(X)  uses  only  the  diagonal
      and upper triangle of  X .  The lower triangular is assumed
      to be the (complex conjugate) transpose of the  upper.   If
      X   is  positive  definite,  then  R = CHOL(X)  produces an
      upper triangular  R  so that  R'*R = X .   If   X   is  not
      positive definite, an error message is printed.

CHOP  Truncate arithmetic.  Floating-point  numbers  have  53 bit
      mantissas whose leading bit is not stored since the numbers
      are normalized.  CHOP(P)  truncates the last  4*P  bits  of
      each floating-point number for 0 < P < 13  (any other value
      of P causes full precision to be used.)    CHOP(0) restores
      full precision.

CLEAR Erases all variables, except EPS, FLOP, EYE and RAND.
      X = <>  erases only variable  X .  So does CLEAR X .

COND  Condition number in 2-norm.  COND(X) is the  ratio  of  the
      largest singular value of  X  to the smallest.

CONJG CONJG(X)  is the complex conjugate of  X .

COS   COS(X)  is the cosine of  X .  See FUN .

DET   DET(X)  is the determinant of the square matrix  X .

DIAG  If  V  is  a  row  or  column  vector  with  N  components,
      DIAG(V,K)   is a square matrix of order  N+ABS(K)  with the
      elements of  V  on the K-th diagonal.  K = 0  is  the  main
      diagonal,  K  >  0  is above the main diagonal and K < 0 is
      below the main diagonal.  DIAG(V)  simply puts  V   on  the
      main diagonal.
      eg. DIAG(-M:M) + DIAG(ONES(2*M,1),1) + DIAG(ONES(2*M,1),-1)
      produces a tridiagonal matrix of order 2*M+1 .
      IF  X  is a matrix,  DIAG(X,K)  is a column  vector  formed
      from the elements of the K-th diagonal of  X .
      DIAG(X)  is the main diagonal of  X .
      DIAG(DIAG(X))  is a diagonal matrix .

DIARY DIARY('file') causes a  copy  of  all  subsequent  terminal
      input and most of the resulting output to be written on the
      file. DIARY(0) turns it off.  See FILE.

DISP  DISPLAY(X) prints X  in  a  compact  format.   If  all  the
      elements  of  X  are  integers  between 0 and 51, then X is
      interpreted  as  MATLAB  text  and   printed   accordingly.
      Otherwise,  +  ,  -   and  blank  are printed for positive,
      negative and zero elements.  Imaginary parts are ignored.
      DISP(X,B) is the same as DISP(BASE(X,B)).

EDIT  There  are  no   editing   features   available   on   most
      installations and EDIT is not a command.  However, on a few
      systems a command line consisting of a single  backslash  \
      will  cause  the local file editor to be called with a copy
      of the  previous  input  line.   When  the  editor  returns
      control to MATLAB, it will execute the line again.

EIG   Eigenvalues and eigenvectors.
      EIG(X) is a vector containing the eigenvalues of  a  square
      matrix  X .
      <V,D>  =  EIG(X)   produces  a  diagonal  matrix    D    of
      eigenvalues  and  a  full  matrix  V  whose columns are the
      corresponding eigenvectors so that  X*V = V*D .

ELSE  Used with IF .

END   Terminates the scope  of  FOR,  WHILE  and  IF  statements.
      Without  END's,  FOR  and WHILE repeat all statements up to
      the end of the line.  Each END is paired with  the  closest
      previous  unpaired FOR or WHILE and serves to terminate its
      scope.  The line
      FOR I=1:N, FOR J=1:N, A(I,J)=1/(I+J-1); A
      would cause A to be printed  N**2  times, once for each new
      element.  On the other hand, the line
      FOR I=1:N, FOR J=1:N, A(I,J)=1/(I+J-1); END, END, A
      will lead to only the final printing of  A .
      Similar considerations apply to WHILE.
      EXIT terminates execution of loops or of MATLAB itself.

EPS   Floating point relative  accuracy.   A  permanent  variable
      whose  value is initially the distance from 1.0 to the next
      largest floating point number.  The  value  is  changed  by
      CHOP,  and  other values may be assigned.  EPS is used as a
      default tolerance by PINV and RANK.

EXEC  EXEC('file',k) obtains  subsequent  MATLAB  input  from  an
      external  file.  The printing of input is controlled by the
      optional parameter k .
      If k = 1 , the input is echoed.
      If k = 2 , the MATLAB prompt <> is printed.
      If k = 4 , MATLAB pauses before each prompt and waits for a
      null line to continue.
      If k = 0 , there is no echo, prompt or pause.  This is  the
      default if the exec command is followed by a semicolon.
      If k = 7 , there will be echos, prompts and pauses. This is
      useful for demonstrations on video terminals.
      If k = 3 , there will be echos and prompts, but no  pauses.
      This is the the default if the exec command is not followed
      by a semicolon.
      EXEC(0) causes subsequent input to  be  obtained  from  the
      terminal. An end-of-file has the same effect.
      EXEC's may be nested, i.e. the text in the file may contain
      EXEC of another file.  EXEC's may also be driven by FOR and
      WHILE loops.

EXIT  Causes termination of a FOR or WHILE loop.
      If not in a loop, terminates execution of MATLAB.

EXP   EXP(X)  is the exponential of  X ,  e  to the X .  See  FUN
      .

EYE   Identity matrix.  EYE(N) is the N  by  N  identity  matrix.
      EYE(M,N)   is an M by N matrix with 1's on the diagonal and
      zeros elsewhere.  EYE(A)  is the same size  as   A  .   EYE
      with  no  arguments is an identity matrix of whatever order
      is appropriate in the context.   For  example,  A  +  3*EYE
      adds  3  to each diagonal element of  A .

FILE  The EXEC, SAVE, LOAD,  PRINT  and  DIARY  functions  access
      files.   The  'file'  parameter  takes  different forms for
      different operating systems.  On most systems,  'file'  may
      be a string of up to 32 characters in quotes.  For example,
      SAVE('A') or EXEC('matlab/demo.exec') .  The string will be
      used as the name of a file in the local operating system.
      On all systems, 'file' may be a positive integer   k   less
      than  10  which  will  be  used  as  a FORTRAN logical unit
      number. Some systems then automatically access a file  with
      a  name  like  FORT.k  or FORk.DAT. Other systems require a
      file with a name like FT0kF001 to be assigned  to  unit   k
      before  MATLAB  is  executed. Check your local installation
      for details.

FLOPS Count of floating point operations.
      FLOPS  is  a  permanently  defined  row  vector  with   two
      elements.    FLOPS(1)  is  the  number  of  floating  point
      operations counted during the previous statement.  FLOPS(2)
      is  a  cumulative total.  FLOPS can be used in the same way
      as any other vector.  FLOPS(2) = 0  resets  the  cumulative
      total.   In  addition,  FLOPS(1) will be printed whenever a
      statement is terminated by an extra comma.  For example,
      X = INV(A);,
      or
      COND(A),   (as the last statement on the line).
      HELP FLPS gives more details.

FLPS  More detail on FLOPS.
      It is not feasible to count absolutely all  floating  point
      operations,  but  most  of  the important ones are counted.
      Each multiply and add in a real vector operation such as  a
      dot  product  or  a 'saxpy' counts one flop.  Each multiply
      and add in a complex vector  operation  counts  two  flops.
      Other additions, subtractions and multiplications count one
      flop each if the result is real and two flops if it is not.
      Real  divisions  count one and complex divisions count two.
      Elementary functions count one if real and two if  complex.
      Some examples.  If A and B are real N by N matrices, then
      A + B  counts N**2 flops,
      A*B    counts N**3 flops,
      A**100 counts 99*N**3 flops,
      LU(A)  counts roughly (1/3)*N**3 flops.

FOR   Repeat statements a specific number of times.
      FOR variable = expr, statement, ..., statement, END
      The END at the end of a line may  be  omitted.   The  comma
      before  the  END  may  also be omitted.  The columns of the
      expression are stored one at a time  in  the  variable  and
      then the following statements, up to the END, are executed.
      The expression is often of the form X:Y, in which case  its
      columns  are  simply  scalars.  Some examples (assume N has
      already been assigned a value).
      FOR I = 1:N, FOR J = 1:N, A(I,J) = 1/(I+J-1);
      FOR J = 2:N-1, A(J,J) = J; END; A
      FOR S = 1.0: -0.1: 0.0, ...  steps S with increments of -0.1 .
      FOR E = EYE(N), ...   sets  E  to the unit N-vectors.
      FOR V = A, ...   has the same effect as
      FOR J = 1:N, V = A(:,J); ...  except J is also set here.

FUN   For matrix arguments  X , the  functions  SIN,  COS,  ATAN,
      SQRT,  LOG,  EXP and X**p are computed using eigenvalues  D
      and eigenvectors  V .  If  <V,D> =  EIG(X)   then   f(X)  =
      V*f(D)/V  .   This method may give inaccurate results if  V
      is badly conditioned.  Some idea of  the  accuracy  can  be
      obtained by comparing  X**1  with  X .
      For vector arguments,  the  function  is  applied  to  each
      component.

HESS  Hessenberg form.  The Hessenberg form of a matrix  is  zero
      below the first subdiagonal.  If the matrix is symmetric or
      Hermitian,  the  form  is  tridiagonal.   <P,H>  =  HESS(A)
      produces  a  unitary  matrix P and a Hessenberg matrix H so
      that A = P*H*P'.  By itself, HESS(A) returns H.

HILB  Inverse Hilbert matrix.  HILB(N)  is the inverse of  the  N
      by  N   matrix  with elements  1/(i+j-1), which is a famous
      example of a badly conditioned matrix.  The result is exact
      for  N  less than about 15, depending upon the computer.

IF    Conditionally execute statements.  Simple form...
      IF expression rop expression, statements
      where rop is =, <, >, <=, >=, or  <>  (not  equal)  .   The
      statements  are  executed  once if the indicated comparison
      between the real parts of the first components of  the  two
      expressions  is true, otherwise the statements are skipped.
      Example.
      IF ABS(I-J) = 1, A(I,J) = -1;
      More complicated forms use END in the same way it  is  used
      with FOR and WHILE and use ELSE as an abbreviation for END,
      IF expression not rop expression .  Example
      FOR I = 1:N, FOR J = 1:N, ...
         IF I = J, A(I,J) = 2; ELSE IF ABS(I-J) = 1, A(I,J) = -1; ...
         ELSE A(I,J) = 0;
      An easier way to accomplish the same thing is
      A = 2*EYE(N);
      FOR I = 1:N-1, A(I,I+1) = -1; A(I+1,I) = -1;

IMAG  IMAG(X)  is the imaginary part of  X .

INV   INV(X)  is the inverse of the square matrix  X .  A warning
      message  is  printed  if   X   is  badly  scaled  or nearly
      singular.

KRON  KRON(X,Y) is the Kronecker tensor product of X and Y  .  It
      is  also  denoted by X .*. Y . The result is a large matrix
      formed by taking all possible products between the elements
      of  X  and  those  of Y . For example, if X is 2 by 3, then
      X .*. Y is

            < x(1,1)*Y  x(1,2)*Y  x(1,3)*Y
              x(2,1)*Y  x(2,2)*Y  x(2,3)*Y >

      The five-point discrete Laplacian for an n-by-n grid can be
      generated by

            T = diag(ones(n-1,1),1);  T = T + T';  I = EYE(T);
            A = T.*.I + I.*.T - 4*EYE;

      Just  in  case  they  might  be  useful,  MATLAB   includes
      constructions called Kronecker tensor quotients, denoted by
      X ./. Y and X .\. Y .  They are obtained by  replacing  the
      elementwise multiplications in X .*. Y with divisions.

LINES An internal count is kept of the number of lines of  output
      since  the  last  input.   Whenever this count approaches a
      limit, the  user  is  asked  whether  or  not  to  suppress
      printing  until the next input.  Initially the limit is 25.
      LINES(N) resets the limit to N .

LOAD  LOAD('file') retrieves all the variables from  the  file  .
      See  FILE  and  SAVE for more details.  To prepare your own
      file for LOADing, change the READs to WRITEs  in  the  code
      given under SAVE.

LOG   LOG(X)  is the  natural  logarithm  of   X  .   See  FUN  .
      Complex results are produced if  X  is not positive, or has
      nonpositive eigenvalues.

LONG  Determine output format.   All  computations  are  done  in
      complex arithmetic and double precision if it is available.
      SHORT and  LONG  merely  switch  between  different  output
      formats.
      SHORT    Scaled fixed point format with about 5 digits.
      LONG     Scaled fixed point format with about 15 digits.
      SHORT E  Floating point format with about 5 digits.
      LONG E   Floating point format with about 15 digits.
      LONG Z   System dependent format, often hexadecimal.

LU    Factors from Gaussian elimination.  <L,U> = LU(X)  stores a
      upper triangular matrix in  U  and a 'psychologically lower
      triangular matrix', i.e. a product of lower triangular  and
      permutation matrices, in L , so that  X = L*U .  By itself,
      LU(X) returns the output from CGEFA .

MACRO The macro facility involves text and inward pointing  angle
      brackets.  If  STRING  is  the  source  text for any MATLAB
      expression or statement, then
            t = 'STRING';
      encodes the text as a vector of integers  and  stores  that
      vector in  t .  DISP(t) will print the text and
            >t<
      causes the text to be interpreted, either as a statement or
      as a factor in an expression.  For example
            t = '1/(i+j-1)';
            disp(t)
            for i = 1:n, for j = 1:n, a(i,j) = >t<;
      generates the Hilbert matrix of order n.
      Another example showing indexed text,
            S = <'x = 3            '
                 'y = 4            '
                 'z = sqrt(x*x+y*y)'>
            for k = 1:3, >S(k,:)<
      It is necessary that the strings making up  the  "rows"  of
      the "matrix"  S  have the same lengths.

MAGIC Magic square.  MAGIC(N) is an N  by  N  matrix  constructed
      from  the integers 1 through N**2 with equal row and column
      sums.

NORM  For matrices..
      NORM(X)  is the largest singular value of  X .
      NORM(X,1)  is the 1-norm of  X .
      NORM(X,2)  is the same as NORM(X) .
      NORM(X,'INF')  is the infinity norm of  X .
      NORM(X,'FRO')  is the F-norm, i.e.  SQRT(SUM(DIAG(X'*X))) .
      For vectors..
      NORM(V,P) = (SUM(V(I)**P))**(1/P) .
      NORM(V) = NORM(V,2) .
      NORM(V,'INF') = MAX(ABS(V(I))) .

ONES  All ones.  ONES(N)  is an N by N matrix of ones.  ONES(M,N)
      is an M by N matrix of ones .  ONES(A)  is the same size as
      A  and all ones .

ORTH  Orthogonalization.   Q  =  ORTH(X)   is   a   matrix   with
      orthonormal  columns,  i.e. Q'*Q = EYE, which span the same
      space as the columns of  X .

PINV  Pseudoinverse.  X = PINV(A) produces a matrix   X   of  the
      same  dimensions as  A' so that  A*X*A = A , X*A*X = X  and
      AX  and  XA  are Hermitian .  The computation is  based  on
      SVD(A)  and  any  singular values less than a tolerance are
      treated   as    zero.     The    default    tolerance    is
      NORM(SIZE(A),'inf')*NORM(A)*EPS.   This  tolerance  may  be
      overridden with X = PINV(A,tol).  See RANK.

PLOT  PLOT(X,Y) produces a plot of  the  elements  of  Y  against
      those  of X . PLOT(Y) is the same as PLOT(1:n,Y) where n is
      the  number  of   elements   in   Y   .    PLOT(X,Y,P)   or
      PLOT(X,Y,p1,...,pk)  passes the optional parameter vector P
      or scalars p1 through pk to the plot routine.  The  default
      plot  routine  is a crude printer-plot. It is hoped that an
      interface to local graphics equipment can be provided.
      An interesting example is
            t = 0:50;
            PLOT( t.*cos(t), t.*sin(t) )

POLY  Characteristic polynomial.
      If  A  is an N by N matrix, POLY(A) is a column vector with
      N+1   elements   which   are   the   coefficients   of  the
      characteristic polynomial,  DET(lambda*EYE - A) .
      If V is a vector, POLY(V) is a vector  whose  elements  are
      the  coefficients  of  the  polynomial  whose roots are the
      elements of V .  For vectors, ROOTS and  POLY  are  inverse
      functions  of  each  other,  up  to  ordering, scaling, and
      roundoff error.
      ROOTS(POLY(1:20)) generates Wilkinson's famous example.

PRINT PRINT('file',X) prints X on  the  file  using  the  current
      format determined by SHORT, LONG Z, etc.  See FILE.

PROD  PROD(X)  is the product of all the elements of  X .

QR    Orthogonal-triangular decomposition.
      <Q,R> = QR(X)  produces an upper triangular  matrix   R  of
      the  same dimension as  X  and a unitary matrix  Q  so that
      X = Q*R .
      <Q,R,E> = QR(X)  produces a  permutation  matrix   E  ,  an
      upper  triangular  R  with decreasing diagonal elements and
      a unitary  Q  so that  X*E = Q*R .
      By itself, QR(X) returns the output of CQRDC .  TRIU(QR(X))
      is R .

RAND  Random numbers and matrices.  RAND(N)  is an N by N  matrix
      with  random  entries.  RAND(M,N)  is an M by N matrix with
      random entries.  RAND(A)  is the same size as   A  .   RAND
      with no arguments is a scalar whose value changes each time
      it is referenced.
      Ordinarily,  random numbers are  uniformly  distributed  in
      the  interval  (0.0,1.0)  .   RAND('NORMAL')  switches to a
      normal distribution  with  mean  0.0  and  variance  1.0  .
      RAND('UNIFORM')  switches back to the uniform distribution.
      RAND('SEED') returns the current value of the seed for  the
      generator.    RAND('SEED',n)   sets   the   seed   to  n  .
      RAND('SEED',0) resets the seed to 0, its value when  MATLAB
      is first entered.

RANK  Rank.  K = RANK(X) is the number of singular values  of   X
      that are larger than NORM(SIZE(X),'inf')*NORM(X)*EPS.
      K = RANK(X,tol) is the number of singular values of  X that
      are larger than tol .

RCOND RCOND(X)   is  an  estimate  for  the  reciprocal  of   the
      condition  of   X   in  the  1-norm obtained by the LINPACK
      condition estimator.  If  X  is well conditioned,  RCOND(X)
      is  near  1.0  .   If  X  is badly conditioned, RCOND(X) is
      near 0.0 .
      <R, Z> = RCOND(A) sets  R  to RCOND(A) and also produces  a
      vector  Z so that
                 NORM(A*Z,1) = R*NORM(A,1)*NORM(Z,1)
      So, if RCOND(A) is small, then  Z  is an  approximate  null
      vector.

RAT   An experimental  function  which  attempts  to  remove  the
      roundoff   error  from  results  that  should  be  "simple"
      rational numbers.
      RAT(X) approximates each  element  of   X  by  a  continued
      fraction of the form

                a/b = d1 + 1/(d2 + 1/(d3 + ... + 1/dk))

      with k <= len, integer di and abs(di) <= max .  The default
      values of the parameters are len = 5 and max = 100.
      RAT(len,max) changes the default values.  Increasing either
      len or max increases the number of possible fractions.
      <A,B> = RAT(X) produces integer matrices A and B so that

                A ./ B  =  RAT(X)

      Some examples:

            long
            T = hilb(6), X = inv(T)
            <A,B> = rat(X)
            H = A ./ B, S = inv(H)

            short e
            d = 1:8,  e = ones(d),  A = abs(d'*e - e'*d)
            X = inv(A)
            rat(X)
            display(ans)


REAL  REAL(X)  is the real part of  X .

RETURN  From the terminal, causes return to the operating  system
      or  other  program  which  invoked  MATLAB.  From inside an
      EXEC, causes  return  to  the  invoking  EXEC,  or  to  the
      terminal.

RREF  RREF(A) is the reduced row echelon form of the  rectangular
      matrix.  RREF(A,B) is the same as RREF(<A,B>) .

ROOTS Find polynomial roots.  ROOTS(C)  computes the roots of the
      polynomial  whose  coefficients  are  the  elements  of the
      vector  C .  If  C  has  N+1  components, the polynomial is
      C(1)*X**N + ... + C(N)*X + C(N+1) .  See POLY.

ROUND ROUND(X)  rounds  the  elements  of   X   to  the   nearest
      integers.

SAVE  SAVE('file') stores all the current variables in a file.
      SAVE('file',X) saves only X .  See FILE .
      The variables may be retrieved later by LOAD('file') or  by
      your  own program using the following code for each matrix.
      The lines involving XIMAG may be eliminated  if  everything
      is known to be real.

            attach lunit to 'file'
            REAL or DOUBLE PRECISION XREAL(MMAX,NMAX)
            REAL or DOUBLE PRECISION XIMAG(MMAX,NMAX)
            READ(lunit,101) ID,M,N,IMG
            DO 10 J = 1, N
               READ(lunit,102) (XREAL(I,J), I=1,M)
               IF (IMG .NE. 0) READ(lunit,102) (XIMAG(I,J),I=1,M)
         10 CONTINUE

      The formats used are system dependent.  The  following  are
      typical.     See    SUBROUTINE   SAVLOD   in   your   local
      implementation of MATLAB.

        101 FORMAT(4A1,3I4)
        102 FORMAT(4Z18)
        102 FORMAT(4O20)
        102 FORMAT(4D25.18)

SCHUR Schur decomposition.  <U,T> = SCHUR(X)  produces  an  upper
      triangular  matrix   T , with the eigenvalues of  X  on the
      diagonal, and a unitary matrix  U so that  X =  U*T*U'  and
      U'*U = EYE .  By itself, SCHUR(X) returns  T .

SHORT See LONG .

SEMI  Semicolons at the end of  lines  will  cause,  rather  than
      suppress,  printing.   A  second  SEMI restores the initial
      interpretation.

SIN   SIN(X)  is the sine of  X .  See FUN .

SIZE  If X is an M by N matrix, then SIZE(X) is <M, N> .
      Can also be used with a multiple assignment,
            <M, N> = SIZE(X) .

SQRT  SQRT(X)  is the square root of  X .   See  FUN  .   Complex
      results  are  produced  if   X   is  not  positive,  or has
      nonpositive eigenvalues.

STOP  Use EXIT instead.

SUM   SUM(X)   is  the  sum  of  all  the  elements   of    X   .
      SUM(DIAG(X))  is the trace of  X .

SVD   Singular value decomposition.  <U,S,V> = SVD(X)  produces a
      diagonal  matrix  S , of the same dimension as  X  and with
      nonnegative diagonal  elements  in  decreasing  order,  and
      unitary matrices  U  and  V  so that  X = U*S*V' .
      By itself, SVD(X) returns a vector containing the  singular
      values.
      <U,S,V>   =   SVD(X,0)   produces   the   "economy    size"
      decomposition.   If  X  is m by n with m > n, then only the
      first n columns of U are computed and S is n by n .

TRIL  Lower triangle.  TRIL(X) is the lower triangular part of X.
      TRIL(X,K) is the elements on and below the K-th diagonal of
      X.  K = 0 is the main diagonal, K > 0  is  above  the  main
      diagonal and K < 0 is below the main diagonal.

TRIU  Upper triangle.  TRIU(X) is the upper triangular part of X.
      TRIU(X,K) is the elements on and above the K-th diagonal of
      X.  K = 0 is the main diagonal, K > 0  is  above  the  main
      diagonal and K < 0 is below the main diagonal.

USER  Allows personal  Fortran  subroutines  to  be  linked  into
      MATLAB .  The subroutine should have the heading

               SUBROUTINE USER(A,M,N,S,T)
               REAL or DOUBLE PRECISION A(M,N),S,T

      The MATLAB statement  Y = USER(X,s,t)  results in a call to
      the  subroutine with a copy of the matrix  X  stored in the
      argument  A , its column and row dimensions in  M  and  N ,
      and  the scalar parameters  s  and  t  stored in  S  and  T
      . If  s and t  are omitted, they are set to  0.0  .   After
      the  return,   A  is stored in  Y .  The dimensions  M  and
      N  may be reset within the subroutine.  The statement  Y  =
      USER(K)  results in a call with M = 1, N = 1  and  A(1,1) =
      FLOAT(K) .  After the subroutine has been written, it  must
      be compiled and linked to the MATLAB object code within the
      local operating system.

WHAT  Lists commands and functions currently available.

WHILE Repeat statements an indefinite number of times.
      WHILE expr rop expr, statement, ..., statement, END
      where rop is =, <, >, <=, >=, or <> (not equal) .  The  END
      at  the end of a line may be omitted.  The comma before the
      END may also be omitted.  The commas  may  be  replaced  by
      semicolons   to   avoid   printing.    The  statements  are
      repeatedly executed as long  as  the  indicated  comparison
      between  the  real parts of the first components of the two
      expressions is true.   Example  (assume  a  matrix   A   is
      already defined).
      E = 0*A; F = E + EYE; N = 1;
      WHILE NORM(E+F-E,1) > 0, E = E + F; F = A*F/N; N = N + 1;
      E

WHO   Lists current variables.

WHY   Provides succinct answers to any questions.

EOF   End of help file.
%