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DTPSV - solve one of the systems of equations A*x = b, or A’*x = b,

SUBROUTINE DTPSV ( UPLO, TRANS, DIAG, N, AP, X, INCX ) INTEGER INCX, N CHARACTER*1 DIAG, TRANS, UPLO DOUBLE PRECISION AP( * ), X( * )

DTPSV 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, supplied in packed form. 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’ 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. AP - DOUBLE PRECISION array of DIMENSION at least ( ( n*( n + 1 ) )/2 ). Before entry with UPLO = ’U’ or ’u’, the array AP must contain the upper triangular matrix packed sequentially, column by column, so that AP( 1 ) contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 1, 2 ) and a( 2, 2 ) respectively, and so on. Before entry with UPLO = ’L’ or ’l’, the array AP must contain the lower triangular matrix packed sequentially, column by column, so that AP( 1 ) contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 2, 1 ) and a( 3, 1 ) respectively, and so on. Note that when DIAG = ’U’ or ’u’, the diagonal elements of A are not referenced, but are assumed to be unity. Unchanged on exit. X - DOUBLE PRECISION 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.