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*DECK DGEDI
SUBROUTINE DGEDI (A, LDA, N, IPVT, DET, WORK, JOB)
C***BEGIN PROLOGUE DGEDI
C***PURPOSE Compute the determinant and inverse of a matrix using the
C factors computed by DGECO or DGEFA.
C***LIBRARY SLATEC (LINPACK)
C***CATEGORY D3A1, D2A1
C***TYPE DOUBLE PRECISION (SGEDI-S, DGEDI-D, CGEDI-C)
C***KEYWORDS DETERMINANT, INVERSE, LINEAR ALGEBRA, LINPACK, MATRIX
C***AUTHOR Moler, C. B., (U. of New Mexico)
C***DESCRIPTION
C
C DGEDI computes the determinant and inverse of a matrix
C using the factors computed by DGECO or DGEFA.
C
C On Entry
C
C A DOUBLE PRECISION(LDA, N)
C the output from DGECO or DGEFA.
C
C LDA INTEGER
C the leading dimension of the array A .
C
C N INTEGER
C the order of the matrix A .
C
C IPVT INTEGER(N)
C the pivot vector from DGECO or DGEFA.
C
C WORK DOUBLE PRECISION(N)
C work vector. Contents destroyed.
C
C JOB INTEGER
C = 11 both determinant and inverse.
C = 01 inverse only.
C = 10 determinant only.
C
C On Return
C
C A inverse of original matrix if requested.
C Otherwise unchanged.
C
C DET DOUBLE PRECISION(2)
C determinant of original matrix if requested.
C Otherwise not referenced.
C Determinant = DET(1) * 10.0**DET(2)
C with 1.0 .LE. ABS(DET(1)) .LT. 10.0
C or DET(1) .EQ. 0.0 .
C
C Error Condition
C
C A division by zero will occur if the input factor contains
C a zero on the diagonal and the inverse is requested.
C It will not occur if the subroutines are called correctly
C and if DGECO has set RCOND .GT. 0.0 or DGEFA has set
C INFO .EQ. 0 .
C
C***REFERENCES J. J. Dongarra, J. R. Bunch, C. B. Moler, and G. W.
C Stewart, LINPACK Users' Guide, SIAM, 1979.
C***ROUTINES CALLED DAXPY, DSCAL, DSWAP
C***REVISION HISTORY (YYMMDD)
C 780814 DATE WRITTEN
C 890531 Changed all specific intrinsics to generic. (WRB)
C 890831 Modified array declarations. (WRB)
C 890831 REVISION DATE from Version 3.2
C 891214 Prologue converted to Version 4.0 format. (BAB)
C 900326 Removed duplicate information from DESCRIPTION section.
C (WRB)
C 920501 Reformatted the REFERENCES section. (WRB)
C***END PROLOGUE DGEDI
INTEGER LDA,N,IPVT(*),JOB
DOUBLE PRECISION A(LDA,*),DET(2),WORK(*)
C
DOUBLE PRECISION T
DOUBLE PRECISION TEN
INTEGER I,J,K,KB,KP1,L,NM1
C***FIRST EXECUTABLE STATEMENT DGEDI
C
C COMPUTE DETERMINANT
C
IF (JOB/10 .EQ. 0) GO TO 70
DET(1) = 1.0D0
DET(2) = 0.0D0
TEN = 10.0D0
DO 50 I = 1, N
IF (IPVT(I) .NE. I) DET(1) = -DET(1)
DET(1) = A(I,I)*DET(1)
IF (DET(1) .EQ. 0.0D0) GO TO 60
10 IF (ABS(DET(1)) .GE. 1.0D0) GO TO 20
DET(1) = TEN*DET(1)
DET(2) = DET(2) - 1.0D0
GO TO 10
20 CONTINUE
30 IF (ABS(DET(1)) .LT. TEN) GO TO 40
DET(1) = DET(1)/TEN
DET(2) = DET(2) + 1.0D0
GO TO 30
40 CONTINUE
50 CONTINUE
60 CONTINUE
70 CONTINUE
C
C COMPUTE INVERSE(U)
C
IF (MOD(JOB,10) .EQ. 0) GO TO 150
DO 100 K = 1, N
A(K,K) = 1.0D0/A(K,K)
T = -A(K,K)
CALL DSCAL(K-1,T,A(1,K),1)
KP1 = K + 1
IF (N .LT. KP1) GO TO 90
DO 80 J = KP1, N
T = A(K,J)
A(K,J) = 0.0D0
CALL DAXPY(K,T,A(1,K),1,A(1,J),1)
80 CONTINUE
90 CONTINUE
100 CONTINUE
C
C FORM INVERSE(U)*INVERSE(L)
C
NM1 = N - 1
IF (NM1 .LT. 1) GO TO 140
DO 130 KB = 1, NM1
K = N - KB
KP1 = K + 1
DO 110 I = KP1, N
WORK(I) = A(I,K)
A(I,K) = 0.0D0
110 CONTINUE
DO 120 J = KP1, N
T = WORK(J)
CALL DAXPY(N,T,A(1,J),1,A(1,K),1)
120 CONTINUE
L = IPVT(K)
IF (L .NE. K) CALL DSWAP(N,A(1,K),1,A(1,L),1)
130 CONTINUE
140 CONTINUE
150 CONTINUE
RETURN
END
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