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C FUNCTION DETERM.F
C
C SOURCE
C BEVINGTON, PAGE 294.
C
C PURPOSE
C CALCULATE THE DETERMINANT OF A SQUARE MATRIX
C
C USAGE
C DET = DETERM (ARRAY, NORDER)
C
C DESCRIPTION OF PARAMETERS
C ARRAY - MATRIX
C NORDER - ORDER OF DETERMINANT (DEGREE OF MATRIX)
C
C SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
C NONE
C
C COMMENTS
C THIS SUBPROGRAM DESTROYS THE INPUT MATRIX ARRAY
C DIMENSION STATEMENT VALID FOR NORDER UP TO 10
C
FUNCTION DETERM (ARRAY,NORDER)
DOUBLE PRECISION ARRAY,SAVE
DIMENSION ARRAY(10,10)
C
10 DETERM=1.
11 DO 50 K=1,NORDER
C
C INTERCHANGE COLUMNS IF DIAGONAL ELEMENT IS ZERO
C
IF (ARRAY(K,K)) 41,21,41
21 DO 23 J=K,NORDER
IF (ARRAY(K,J)) 31,23,31
23 CONTINUE
DETERM=0.
GOTO 60
31 DO 34 I=K,NORDER
SAVE=ARRAY(I,J)
ARRAY(I,J)=ARRAY(I,K)
34 ARRAY(I,K)=SAVE
DETERM=-DETERM
C
C SUBTRACT ROW K FROM LOWER ROWS TO GET DIAGONAL MATRIX
C
41 DETERM=DETERM*ARRAY(K,K)
IF (K-NORDER) 43,50,50
43 K1=K+1
DO 46 I=K1,NORDER
DO 46 J=K1,NORDER
46 ARRAY(I,J)=ARRAY(I,J)-ARRAY(I,K)*ARRAY(K,J)/ARRAY(K,K)
50 CONTINUE
60 RETURN
END
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