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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, * ) 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 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). (LDB,NRHS) B (input/output) DOUBLE PRECISION array, dimension 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.