stptrs(3)

NAME

STPTRS - solve a triangular system of the form A * X = B

or A**T * X = B,

SYNOPSIS

SUBROUTINE STPTRS( UPLO, TRANS, DIAG, N, NRHS, AP, B, LDB,
INFO )
    CHARACTER      DIAG, TRANS, UPLO
    INTEGER        INFO, LDB, N, NRHS
    REAL           AP( * ), B( LDB, * )

PURPOSE

STPTRS 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) REAL 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.

B (input/output) REAL 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.

LAPACK version 3.0 15 June 2000

STPTRS(3)