DTRSL(3)

SYNOPSIS
SUBROUTINE DTRSL (T, LDT, N, B, JOB, INFO)

NAME
dtrsl - Solve a system of the form T*X=B or TRANS(T)*X=B, where T is a triangular matrix.

LIBRARY
SLATEC (LINPACK)

CATEGORY
D2A3

TYPE
DOUBLE PRECISION (STRSL-S, DTRSL-D, CTRSL-C)

KEYWORDS
LINEAR ALGEBRA, LINPACK, TRIANGULAR LINEAR SYSTEM, TRIANGULAR MATRIX

AUTHOR
Stewart, G. W., (U. of Maryland)

DESCRIPTION
DTRSL solves systems of the form T * X = B or TRANS(T) * X = B where T is a triangular matrix of order N. Here TRANS(T) denotes the transpose of the matrix T. On Entry T DOUBLE PRECISION(LDT,N) T contains the matrix of the system. 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. B DOUBLE PRECISION(N). B contains the right hand side of the system. JOB INTEGER JOB specifies what kind of system is to be solved. If JOB is 00 solve T*X=B, T lower triangular, 01 solve T*X=B, T upper triangular, 10 solve TRANS(T)*X=B, T lower triangular, 11 solve TRANS(T)*X=B, T upper triangular. On Return B B contains the solution, if INFO .EQ. 0. Otherwise B is unaltered. INFO INTEGER INFO contains zero if the system is nonsingular. Otherwise INFO contains the index of the first 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, DDOT

REVISION HISTORY (YYMMDD)
780814 DATE WRITTEN
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)