Previous: cporfs Up: ../lapack-c.html Next: cposvx

# cposv

```
NAME
CPOSV - compute the solution to a complex system of linear
equations  A * X = B,

SYNOPSIS
SUBROUTINE CPOSV( UPLO, N, NRHS, A, LDA, B, LDB, INFO )

CHARACTER     UPLO

INTEGER       INFO, LDA, LDB, N, NRHS

COMPLEX       A( LDA, * ), B( LDB, * )

PURPOSE
CPOSV computes the solution to a complex system of linear
equations
A * X = B, where A is an N-by-N Hermitian positive defin-
ite matrix and X and B are N-by-NRHS matrices.

The Cholesky decomposition is used to factor A as
A = U**H* U,  if UPLO = 'U', or
A = L * L**H,  if UPLO = 'L',
where U is an upper triangular matrix and  L is a lower tri-
angular matrix.  The factored form of A is then used to
solve the system of equations A * X = B.

ARGUMENTS
UPLO    (input) CHARACTER*1
= 'U':  Upper triangle of A is stored;
= 'L':  Lower triangle of A is stored.

N       (input) INTEGER
The number of linear equations, i.e., 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.

A       (input/output) COMPLEX array, dimension (LDA,N)
On entry, the Hermitian matrix A.  If UPLO = 'U',
the leading N-by-N upper triangular part of A con-
tains the upper triangular part of the matrix A, and
the strictly lower triangular part of A is not
referenced.  If UPLO = 'L', the leading N-by-N lower
triangular part of A contains the lower triangular
part of the matrix A, and the strictly upper tri-
angular part of A is not referenced.

On exit, if INFO = 0, the factor U or L from the
Cholesky factorization A = U**H*U or A = L*L**H.

LDA     (input) INTEGER
The leading dimension of the array A.  LDA >=
max(1,N).

B       (input/output) COMPLEX array, dimension (LDB,NRHS)
On entry, the N-by-NRHS right hand side matrix B.
On exit, if INFO = 0, the N-by-NRHS 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 leading minor of order i of A
is not positive definite, so the factorization could
not be completed, and the solution has not been com-
puted.
```