DTPTRS - solve a triangular system of the form A * X = B
or A**T * X = B,
SYNOPSIS
SUBROUTINE DTPTRS( UPLO, TRANS, DIAG, N, NRHS, AP, B, LDB,
INFO )
CHARACTER DIAG, TRANS, UPLO
INTEGER INFO, LDB, N, NRHS
DOUBLE PRECISION AP( * ), B( LDB, * )
PURPOSE
DTPTRS solves a triangular system of the form A * X = B or
A**T * X = B, where A is a triangular matrix of order N
stored in packed format, 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.
AP (input) DOUBLE PRECISION array, dimension
(N*(N+1)/2)
The upper or lower triangular matrix A, packed
columnwise in a linear array. The j-th column of
A is stored in the array AP as follows: if UPLO =
'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j; if
UPLO = 'L', AP(i + (j-1)*(2*n-j)/2) = A(i,j) for
j<=i<=n.
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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