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147 lines
4.9 KiB
Fortran
147 lines
4.9 KiB
Fortran
*DECK DTRDI
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SUBROUTINE DTRDI (T, LDT, N, DET, JOB, INFO)
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C***BEGIN PROLOGUE DTRDI
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C***PURPOSE Compute the determinant and inverse of a triangular matrix.
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C***LIBRARY SLATEC (LINPACK)
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C***CATEGORY D2A3, D3A3
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C***TYPE DOUBLE PRECISION (STRDI-S, DTRDI-D, CTRDI-C)
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C***KEYWORDS DETERMINANT, INVERSE, LINEAR ALGEBRA, LINPACK,
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C TRIANGULAR MATRIX
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C***AUTHOR Moler, C. B., (U. of New Mexico)
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C***DESCRIPTION
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C
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C DTRDI computes the determinant and inverse of a double precision
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C triangular matrix.
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C
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C On Entry
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C
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C T DOUBLE PRECISION(LDT,N)
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C T contains the triangular matrix. The zero
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C elements of the matrix are not referenced, and
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C the corresponding elements of the array can be
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C used to store other information.
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C
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C LDT INTEGER
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C LDT is the leading dimension of the array T.
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C
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C N INTEGER
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C N is the order of the system.
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C
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C JOB INTEGER
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C = 010 no det, inverse of lower triangular.
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C = 011 no det, inverse of upper triangular.
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C = 100 det, no inverse.
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C = 110 det, inverse of lower triangular.
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C = 111 det, inverse of upper triangular.
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C
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C On Return
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C
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C T inverse of original matrix if requested.
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C Otherwise unchanged.
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C
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C DET DOUBLE PRECISION(2)
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C determinant of original matrix if requested.
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C Otherwise not referenced.
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C DETERMINANT = DET(1) * 10.0**DET(2)
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C with 1.0 .LE. ABS(DET(1)) .LT. 10.0
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C or DET(1) .EQ. 0.0 .
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C
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C INFO INTEGER
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C INFO contains zero if the system is nonsingular
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C and the inverse is requested.
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C Otherwise INFO contains the index of
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C a zero diagonal element of T.
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C
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C
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C***REFERENCES J. J. Dongarra, J. R. Bunch, C. B. Moler, and G. W.
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C Stewart, LINPACK Users' Guide, SIAM, 1979.
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C***ROUTINES CALLED DAXPY, DSCAL
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C***REVISION HISTORY (YYMMDD)
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C 780814 DATE WRITTEN
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C 890531 Changed all specific intrinsics to generic. (WRB)
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C 890831 Modified array declarations. (WRB)
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C 890831 REVISION DATE from Version 3.2
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C 891214 Prologue converted to Version 4.0 format. (BAB)
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C 900326 Removed duplicate information from DESCRIPTION section.
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C (WRB)
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C 920501 Reformatted the REFERENCES section. (WRB)
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C***END PROLOGUE DTRDI
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INTEGER LDT,N,JOB,INFO
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DOUBLE PRECISION T(LDT,*),DET(2)
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C
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DOUBLE PRECISION TEMP
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DOUBLE PRECISION TEN
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INTEGER I,J,K,KB,KM1,KP1
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C***FIRST EXECUTABLE STATEMENT DTRDI
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C
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C COMPUTE DETERMINANT
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C
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IF (JOB/100 .EQ. 0) GO TO 70
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DET(1) = 1.0D0
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DET(2) = 0.0D0
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TEN = 10.0D0
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DO 50 I = 1, N
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DET(1) = T(I,I)*DET(1)
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IF (DET(1) .EQ. 0.0D0) GO TO 60
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10 IF (ABS(DET(1)) .GE. 1.0D0) GO TO 20
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DET(1) = TEN*DET(1)
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DET(2) = DET(2) - 1.0D0
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GO TO 10
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20 CONTINUE
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30 IF (ABS(DET(1)) .LT. TEN) GO TO 40
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DET(1) = DET(1)/TEN
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DET(2) = DET(2) + 1.0D0
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GO TO 30
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40 CONTINUE
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50 CONTINUE
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60 CONTINUE
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70 CONTINUE
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C
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C COMPUTE INVERSE OF UPPER TRIANGULAR
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C
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IF (MOD(JOB/10,10) .EQ. 0) GO TO 170
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IF (MOD(JOB,10) .EQ. 0) GO TO 120
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DO 100 K = 1, N
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INFO = K
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IF (T(K,K) .EQ. 0.0D0) GO TO 110
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T(K,K) = 1.0D0/T(K,K)
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TEMP = -T(K,K)
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CALL DSCAL(K-1,TEMP,T(1,K),1)
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KP1 = K + 1
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IF (N .LT. KP1) GO TO 90
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DO 80 J = KP1, N
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TEMP = T(K,J)
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T(K,J) = 0.0D0
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CALL DAXPY(K,TEMP,T(1,K),1,T(1,J),1)
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80 CONTINUE
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90 CONTINUE
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100 CONTINUE
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INFO = 0
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110 CONTINUE
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GO TO 160
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120 CONTINUE
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C
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C COMPUTE INVERSE OF LOWER TRIANGULAR
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C
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DO 150 KB = 1, N
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K = N + 1 - KB
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INFO = K
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IF (T(K,K) .EQ. 0.0D0) GO TO 180
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T(K,K) = 1.0D0/T(K,K)
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TEMP = -T(K,K)
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IF (K .NE. N) CALL DSCAL(N-K,TEMP,T(K+1,K),1)
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KM1 = K - 1
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IF (KM1 .LT. 1) GO TO 140
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DO 130 J = 1, KM1
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TEMP = T(K,J)
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T(K,J) = 0.0D0
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CALL DAXPY(N-K+1,TEMP,T(K,K),1,T(K,J),1)
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130 CONTINUE
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140 CONTINUE
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150 CONTINUE
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INFO = 0
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160 CONTINUE
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170 CONTINUE
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180 CONTINUE
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RETURN
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END
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