# chpgst.f man page

chpgst.f —

## Synopsis

### Functions/Subroutines

subroutinechpgst(ITYPE, UPLO, N, AP, BP, INFO)CHPGST

## Function/Subroutine Documentation

### subroutine chpgst (integerITYPE, characterUPLO, integerN, complex, dimension( * )AP, complex, dimension( * )BP, integerINFO)

**CHPGST**

**Purpose:**

```
CHPGST reduces a complex Hermitian-definite generalized
eigenproblem to standard form, using packed storage.
If ITYPE = 1, the problem is A*x = lambda*B*x,
and A is overwritten by inv(U**H)*A*inv(U) or inv(L)*A*inv(L**H)
If ITYPE = 2 or 3, the problem is A*B*x = lambda*x or
B*A*x = lambda*x, and A is overwritten by U*A*U**H or L**H*A*L.
B must have been previously factorized as U**H*U or L*L**H by CPPTRF.
```

**Parameters:**

*ITYPE*

```
ITYPE is INTEGER
= 1: compute inv(U**H)*A*inv(U) or inv(L)*A*inv(L**H);
= 2 or 3: compute U*A*U**H or L**H*A*L.
```

*UPLO*

```
UPLO is CHARACTER*1
= 'U': Upper triangle of A is stored and B is factored as
U**H*U;
= 'L': Lower triangle of A is stored and B is factored as
L*L**H.
```

*N*

```
N is INTEGER
The order of the matrices A and B. N >= 0.
```

*AP*

```
AP is COMPLEX array, dimension (N*(N+1)/2)
On entry, the upper or lower triangle of the Hermitian 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)*(2n-j)/2) = A(i,j) for j<=i<=n.
On exit, if INFO = 0, the transformed matrix, stored in the
same format as A.
```

*BP*

```
BP is COMPLEX array, dimension (N*(N+1)/2)
The triangular factor from the Cholesky factorization of B,
stored in the same format as A, as returned by CPPTRF.
```

*INFO*

```
INFO is INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
```

**Author:**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**

November 2011

Definition at line 114 of file chpgst.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

chpgst(3) is an alias of chpgst.f(3).