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DALI.FOR
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1985-11-29
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112 lines
C
C ..................................................................
C
C SUBROUTINE DALI
C
C PURPOSE
C TO INTERPOLATE FUNCTION VALUE Y FOR A GIVEN ARGUMENT VALUE
C X USING A GIVEN TABLE (ARG,VAL) OF ARGUMENT AND FUNCTION
C VALUES.
C
C USAGE
C CALL DALI (X,ARG,VAL,Y,NDIM,EPS,IER)
C
C DESCRIPTION OF PARAMETERS
C X - DOUBLE PRECISION ARGUMENT VALUE SPECIFIED BY INPUT.
C ARG - DOUBLE PRECISION INPUT VECTOR (DIMENSION NDIM) OF
C ARGUMENT VALUES OF THE TABLE (NOT DESTROYED).
C VAL - DOUBLE PRECISION INPUT VECTOR (DIMENSION NDIM) OF
C FUNCTION VALUES OF THE TABLE (DESTROYED).
C Y - RESULTING INTERPOLATED DOUBLE PRECISION FUNCTION
C VALUE.
C NDIM - AN INPUT VALUE WHICH SPECIFIES THE NUMBER OF
C POINTS IN TABLE (ARG,VAL).
C EPS - SINGLE PRECISION INPUT CONSTANT WHICH IS USED AS
C UPPER BOUND FOR THE ABSOLUTE ERROR.
C FOR THE ABSOLUTE ERROR.
C IER - A RESULTING ERROR PARAMETER.
C
C REMARKS
C (1) TABLE (ARG,VAL) SHOULD REPRESENT A SINGLE-VALUED
C FUNCTION AND SHOULD BE STORED IN SUCH A WAY, THAT THE
C DISTANCES ABS(ARG(I)-X) INCREASE WITH INCREASING
C SUBSCRIPT I. TO GENERATE THIS ORDER IN TABLE (ARG,VAL),
C SUBROUTINES DATSG, DATSM OR DATSE COULD BE USED IN A
C PREVIOUS STAGE.
C (2) NO ACTION BESIDES ERROR MESSAGE IN CASE NDIM LESS
C THAN 1.
C (3) INTERPOLATION IS TERMINATED EITHER IF THE DIFFERENCE
C BETWEEN TWO SUCCESSIVE INTERPOLATED VALUES IS
C ABSOLUTELY LESS THAN TOLERANCE EPS, OR IF THE ABSOLUTE
C VALUE OF THIS DIFFERENCE STOPS DIMINISHING, OR AFTER
C (NDIM-1) STEPS. FURTHER IT IS TERMINATED IF THE
C PROCEDURE DISCOVERS TWO ARGUMENT VALUES IN VECTOR ARG
C WHICH ARE IDENTICAL. DEPENDENT ON THESE FOUR CASES,
C ERROR PARAMETER IER IS CODED IN THE FOLLOWING FORM
C IER=0 - IT WAS POSSIBLE TO REACH THE REQUIRED
C ACCURACY (NO ERROR).
C IER=1 - IT WAS IMPOSSIBLE TO REACH THE REQUIRED
C ACCURACY BECAUSE OF ROUNDING ERRORS.
C IER=2 - IT WAS IMPOSSIBLE TO CHECK ACCURACY BECAUSE
C NDIM IS LESS THAN 3, OR THE REQUIRED ACCURACY
C COULD NOT BE REACHED BY MEANS OF THE GIVEN
C TABLE. NDIM SHOULD BE INCREASED.
C IER=3 - THE PROCEDURE DISCOVERED TWO ARGUMENT VALUES
C IN VECTOR ARG WHICH ARE IDENTICAL.
C
C SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
C NONE
C
C METHOD
C INTERPOLATION IS DONE BY MEANS OF AITKENS SCHEME OF
C LAGRANGE INTERPOLATION. ON RETURN Y CONTAINS AN INTERPOLATED
C FUNCTION VALUE AT POINT X, WHICH IS IN THE SENSE OF REMARK
C (3) OPTIMAL WITH RESPECT TO GIVEN TABLE. FOR REFERENCE, SEE
C F.B.HILDEBRAND, INTRODUCTION TO NUMERICAL ANALYSIS,
C MCGRAW-HILL, NEW YORK/TORONTO/LONDON, 1956, PP.49-50.
C
C ..................................................................
C
SUBROUTINE DALI(X,ARG,VAL,Y,NDIM,EPS,IER)
C
C
DIMENSION ARG(1),VAL(1)
DOUBLE PRECISION ARG,VAL,X,Y,H
IER=2
DELT2=0.
IF(NDIM-1)9,7,1
C
C START OF AITKEN-LOOP
1 DO 6 J=2,NDIM
DELT1=DELT2
IEND=J-1
DO 2 I=1,IEND
H=ARG(I)-ARG(J)
IF(H)2,13,2
2 VAL(J)=(VAL(I)*(X-ARG(J))-VAL(J)*(X-ARG(I)))/H
DELT2=DABS(VAL(J)-VAL(IEND))
IF(J-2)6,6,3
3 IF(DELT2-EPS)10,10,4
4 IF(J-8)6,5,5
5 IF(DELT2-DELT1)6,11,11
6 CONTINUE
C END OF AITKEN-LOOP
C
7 J=NDIM
8 Y=VAL(J)
9 RETURN
C
C THERE IS SUFFICIENT ACCURACY WITHIN NDIM-1 ITERATION STEPS
10 IER=0
GOTO 8
C
C TEST VALUE DELT2 STARTS OSCILLATING
11 IER=1
12 J=IEND
GOTO 8
C
C THERE ARE TWO IDENTICAL ARGUMENT VALUES IN VECTOR ARG
13 IER=3
GOTO 12
END