---
name: "chegst"
section: "3"
platform: "linux"
package: "lapack-doc"
version: "3.12.1-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/chegst.f"
---

# chegst(3)

Part of [chegst.f(3)](/chegst.f/3.md).

## NAME

SRC/chegst.f

## SYNOPSIS

### Functions/Subroutines

subroutine **chegst** (itype, uplo, n, a, lda, b, ldb, info)\
 **CHEGST**

## Function/Subroutine Documentation

### subroutine chegst (integer itype, character uplo, integer n, complex, dimension( lda, \* ) a, integer lda, complex, dimension( ldb, \* ) b, integer ldb, integer info)

**CHEGST**

**Purpose:**

```
!>
!> CHEGST reduces a complex Hermitian-definite generalized
!> eigenproblem to standard form.
!>
!> 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 CPOTRF.
!>
```

**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.
!>
```

*A*

```
!>          A is COMPLEX array, dimension (LDA,N)
!>          On entry, the Hermitian matrix A.  If UPLO = 'U', the leading
!>          N-by-N upper triangular part of A contains 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
!>          triangular part of A is not referenced.
!>
!>          On exit, if INFO = 0, the transformed matrix, stored in the
!>          same format as A.
!>
```

*LDA*

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

*B*

```
!>          B is COMPLEX array, dimension (LDB,N)
!>          The triangular factor from the Cholesky factorization of B,
!>          as returned by CPOTRF.
!>          B is modified by the routine but restored on exit.
!>
```

*LDB*

```
!>          LDB is INTEGER
!>          The leading dimension of the array B.  LDB >= max(1,N).
!>
```

*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.

Definition at line **127** of file **chegst.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.