DTRDI(3)

SYNOPSIS
SUBROUTINE DTRDI (T, LDT, N, DET, JOB, INFO)

NAME
dtrdi - Compute the determinant and inverse of a triangular matrix.

LIBRARY
SLATEC (LINPACK)

CATEGORY
D2A3, D3A3

TYPE
DOUBLE PRECISION (STRDI-S, DTRDI-D, CTRDI-C)

KEYWORDS
DETERMINANT, INVERSE, LINEAR ALGEBRA, LINPACK, TRIANGULAR MATRIX

AUTHOR
Moler, C. B., (U. of New Mexico)

DESCRIPTION
DTRDI computes the determinant and inverse of a double precision triangular matrix. On Entry T DOUBLE PRECISION(LDT,N) T contains the triangular matrix. The zero elements of the matrix are not referenced, and the corresponding elements of the array can be used to store other information. LDT INTEGER LDT is the leading dimension of the array T. N INTEGER N is the order of the system. JOB INTEGER = 010 no det, inverse of lower triangular. = 011 no det, inverse of upper triangular. = 100 det, no inverse. = 110 det, inverse of lower triangular. = 111 det, inverse of upper triangular. On Return T inverse of original matrix if requested. Otherwise unchanged. DET DOUBLE PRECISION(2) determinant of original matrix if requested. Otherwise not referenced. DETERMINANT = DET(1) * 10.0**DET(2) with 1.0 .LE. ABS(DET(1)) .LT. 10.0 or DET(1) .EQ. 0.0 . INFO INTEGER INFO contains zero if the system is nonsingular and the inverse is requested. Otherwise INFO contains the index of a zero diagonal element of T.

REFERENCES
J. J. Dongarra, J. R. Bunch, C. B. Moler, and G. W. Stewart, LINPACK Users' Guide, SIAM, 1979.

ROUTINES CALLED
DAXPY, DSCAL

REVISION HISTORY (YYMMDD)
780814 DATE WRITTEN
890531 Changed all specific intrinsics to generic. (WRB)
890831 Modified array declarations. (WRB)
890831 REVISION DATE from Version 3.2
891214 Prologue converted to Version 4.0 format. (BAB)
900326 Removed duplicate information from DESCRIPTION section. (WRB)
920501 Reformatted the REFERENCES section. (WRB)