dtrtrs(3S)

NAME
     DTRTRS - solve a triangular system of the form  A * X = B or A**T * X =
     B,

SYNOPSIS
     SUBROUTINE DTRTRS( UPLO, TRANS, DIAG, N, NRHS, A, LDA, B, LDB, INFO )

         CHARACTER      DIAG, TRANS, UPLO

         INTEGER        INFO, LDA, LDB, N, NRHS

         DOUBLE         PRECISION A( LDA, * ), B( LDB, * )

IMPLEMENTATION
     These routines are part of the SCSL Scientific Library and can be loaded
     using either the -lscs or the -lscs_mp option.  The -lscs_mp option
     directs the linker to use the multi-processor version of the library.

     When linking to SCSL with -lscs or -lscs_mp, the default integer size is
     4 bytes (32 bits). Another version of SCSL is available in which integers
     are 8 bytes (64 bits).  This version allows the user access to larger
     memory sizes and helps when porting legacy Cray codes.  It can be loaded
     by using the -lscs_i8 option or the -lscs_i8_mp option. A program may use
     only one of the two versions; 4-byte integer and 8-byte integer library
     calls cannot be mixed.

PURPOSE
     DTRTRS solves a triangular system of the form A * X = B or A**T * X = B,
     where A is a triangular matrix of order N, and B is an N-by-NRHS matrix.
     A check is made to verify that A is nonsingular.


ARGUMENTS
     UPLO    (input) CHARACTER*1
             = 'U':  A is upper triangular;
             = 'L':  A is lower triangular.

     TRANS   (input) CHARACTER*1
             Specifies the form of the system of equations:
             = 'N':  A * X = B  (No transpose)
             = 'T':  A**T * X = B  (Transpose)
             = 'C':  A**H * X = B  (Conjugate transpose = Transpose)

     DIAG    (input) CHARACTER*1
             = 'N':  A is non-unit triangular;
             = 'U':  A is unit triangular.

     N       (input) INTEGER
             The order of the matrix A.  N >= 0.
     NRHS    (input) INTEGER
             The number of right hand sides, i.e., the number of columns of
             the matrix B.  NRHS >= 0.

     A       (input) DOUBLE PRECISION array, dimension (LDA,N)
             The triangular matrix A.  If UPLO = 'U', the leading N-by-N upper
             triangular part of the array A contains the upper triangular
             matrix, and the strictly lower triangular part of A is not
             referenced.  If UPLO = 'L', the leading N-by-N lower triangular
             part of the array A contains the lower triangular matrix, and the
             strictly upper triangular part of A is not referenced.  If DIAG =
             'U', the diagonal elements of A are also not referenced and are
             assumed to be 1.

     LDA     (input) INTEGER
             The leading dimension of the array A.  LDA >= max(1,N).

     B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
             On entry, the right hand side matrix B.  On exit, if INFO = 0,
             the solution matrix X.

     LDB     (input) INTEGER
             The leading dimension of the array B.  LDB >= max(1,N).

     INFO    (output) INTEGER
             = 0:  successful exit
             < 0: if INFO = -i, the i-th argument had an illegal value
             > 0: if INFO = i, the i-th diagonal element of A is zero,
             indicating that the matrix is singular and the solutions X have
             not been computed.

SEE ALSO
     INTRO_LAPACK(3S), INTRO_SCSL(3S)

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