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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, * )



     #include <sunperf.h>

     void dtrtrs(char uplo, char trans, char  diag,  int  n,  int
               nrhs,  double  *da,  int lda, double *db, int ldb,
               int *info) ;

PURPOSE
     DTRTRS solves a triangular system of the form

     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 non-
     singular.


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 = Tran-
               spose)

     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 lead-
               ing  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 refer-
               enced.  If UPLO = 'L', the  leading  N-by-N  lower
               triangular  part of the array A contains the lower
               triangular matrix, and the strictly upper triangu-
               lar  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  ille-
               gal 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.

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