# dtrsl.f

```      SUBROUTINE DTRSL (T, LDT, N, B, JOB, INFO)
C***BEGIN PROLOGUE  DTRSL
C***PURPOSE  Solve a system of the form  T*X=B or TRANS(T)*X=B, where
C            T is a triangular matrix.
C***LIBRARY   SLATEC (LINPACK)
C***CATEGORY  D2A3
C***TYPE      DOUBLE PRECISION (STRSL-S, DTRSL-D, CTRSL-C)
C***KEYWORDS  LINEAR ALGEBRA, LINPACK, TRIANGULAR LINEAR SYSTEM,
C             TRIANGULAR MATRIX
C***AUTHOR  Stewart, G. W., (U. of Maryland)
C***DESCRIPTION
C
C     DTRSL solves systems of the form
C
C                   T * X = B
C     or
C                   TRANS(T) * X = B
C
C     where T is a triangular matrix of order N.  Here TRANS(T)
C     denotes the transpose of the matrix T.
C
C     On Entry
C
C         T         DOUBLE PRECISION(LDT,N)
C                   T contains the matrix of the system.  The zero
C                   elements of the matrix are not referenced, and
C                   the corresponding elements of the array can be
C                   used to store other information.
C
C         LDT       INTEGER
C                   LDT is the leading dimension of the array T.
C
C         N         INTEGER
C                   N is the order of the system.
C
C         B         DOUBLE PRECISION(N).
C                   B contains the right hand side of the system.
C
C         JOB       INTEGER
C                   JOB specifies what kind of system is to be solved.
C                   If JOB is
C
C                        00   solve T*X=B, T lower triangular,
C                        01   solve T*X=B, T upper triangular,
C                        10   solve TRANS(T)*X=B, T lower triangular,
C                        11   solve TRANS(T)*X=B, T upper triangular.
C
C     On Return
C
C         B         B contains the solution, if INFO .EQ. 0.
C                   Otherwise B is unaltered.
C
C         INFO      INTEGER
C                   INFO contains zero if the system is nonsingular.
C                   Otherwise INFO contains the index of
C                   the first zero diagonal element of T.
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, DDOT
C***REVISION HISTORY  (YYMMDD)
C   780814  DATE WRITTEN
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  DTRSL
```