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CTRSV - solve one of the systems of equations A*x = b, or A’*x = b, or conjg( A’ )*x = b,

SUBROUTINE CTRSV ( UPLO, TRANS, DIAG, N, A, LDA, X, INCX ) INTEGER INCX, LDA, N CHARACTER*1 DIAG, TRANS, UPLO COMPLEX A( LDA, * ), X( * )

CTRSV solves one of the systems of equations where b and x are n element vectors and A is an n by n unit, or non- unit, upper or lower triangular matrix. No test for singularity or near-singularity is included in this routine. Such tests must be performed before calling this routine.

UPLO - CHARACTER*1. On entry, UPLO specifies whether the matrix is an upper or lower triangular matrix as follows: UPLO = ’U’ or ’u’ A is an upper triangular matrix. UPLO = ’L’ or ’l’ A is a lower triangular matrix. Unchanged on exit. TRANS - CHARACTER*1. On entry, TRANS specifies the equations to be solved as follows: TRANS = ’N’ or ’n’ A*x = b. TRANS = ’T’ or ’t’ A’*x = b. TRANS = ’C’ or ’c’ conjg( A’ )*x = b. Unchanged on exit. DIAG - CHARACTER*1. On entry, DIAG specifies whether or not A is unit triangular as follows: DIAG = ’U’ or ’u’ A is assumed to be unit triangular. DIAG = ’N’ or ’n’ A is not assumed to be unit triangular. Unchanged on exit. N - INTEGER. On entry, N specifies the order of the matrix A. N must be at least zero. Unchanged on exit. A - COMPLEX array of DIMENSION ( LDA, n ). Before entry with UPLO = ’U’ or ’u’, the leading n by n upper triangular part of the array A must contain the upper triangular matrix and the strictly lower triangular part of A is not referenced. Before entry with UPLO = ’L’ or ’l’, the leading n by n lower triangular part of the array A must contain the lower triangular matrix and the strictly upper triangular part of A is not referenced. Note that when DIAG = ’U’ or ’u’, the diagonal elements of A are not referenced either, but are assumed to be unity. Unchanged on exit. LDA - INTEGER. On entry, LDA specifies the first dimension of A as declared in the calling (sub) program. LDA must be at least max( 1, n ). Unchanged on exit. X - COMPLEX array of dimension at least ( 1 + ( n - 1 )*abs( INCX ) ). Before entry, the incremented array X must contain the n element right-hand side vector b. On exit, X is overwritten with the solution vector x. INCX - INTEGER. On entry, INCX specifies the increment for the elements of X. INCX must not be zero. Unchanged on exit. Level 2 Blas routine. -- Written on 22-October-1986. Jack Dongarra, Argonne National Lab. Jeremy Du Croz, Nag Central Office. Sven Hammarling, Nag Central Office. Richard Hanson, Sandia National Labs.