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# stptrs

```
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

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 = 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.

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((j-1)*j/2 + i) = A(i,j) for 1<=i<=j; if UPLO =
'L', AP((j-1)*(n-j) + j*(j+1)/2 + i-j) = 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 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.
```