---
name: "chetri_rook"
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/chetri_rook.f"
---

# chetri\_rook(3)

Part of [chetri\_rook.f(3)](/chetri_rook.f/3.md).

## NAME

SRC/chetri\_rook.f

## SYNOPSIS

### Functions/Subroutines

subroutine **chetri\_rook** (uplo, n, a, lda, ipiv, work, info)\
 **CHETRI\_ROOK** computes the inverse of HE matrix using the factorization obtained with the bounded Bunch-Kaufman (*rook")*diagonal*pivoting*method.

## Function/Subroutine Documentation

### subroutine chetri\_rook (character uplo, integer n, complex, dimension( lda, \* ) a, integer lda, integer, dimension( \* ) ipiv, complex, dimension( \* ) work, integer info)

**CHETRI\_ROOK** computes the inverse of HE matrix using the factorization obtained with the bounded Bunch-Kaufman ("rook") diagonal pivoting method.

**Purpose:**

```
!>
!> CHETRI_ROOK computes the inverse of a complex Hermitian indefinite matrix
!> A using the factorization A = U*D*U**H or A = L*D*L**H computed by
!> CHETRF_ROOK.
!>
```

**Parameters**

*UPLO*

```
!>          UPLO is CHARACTER*1
!>          Specifies whether the details of the factorization are stored
!>          as an upper or lower triangular matrix.
!>          = 'U':  Upper triangular, form is A = U*D*U**H;
!>          = 'L':  Lower triangular, form is A = L*D*L**H.
!>
```

*N*

```
!>          N is INTEGER
!>          The order of the matrix A.  N >= 0.
!>
```

*A*

```
!>          A is COMPLEX array, dimension (LDA,N)
!>          On entry, the block diagonal matrix D and the multipliers
!>          used to obtain the factor U or L as computed by CHETRF_ROOK.
!>
!>          On exit, if INFO = 0, the (Hermitian) inverse of the original
!>          matrix.  If UPLO = 'U', the upper triangular part of the
!>          inverse is formed and the part of A below the diagonal is not
!>          referenced; if UPLO = 'L' the lower triangular part of the
!>          inverse is formed and the part of A above the diagonal is
!>          not referenced.
!>
```

*LDA*

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

*IPIV*

```
!>          IPIV is INTEGER array, dimension (N)
!>          Details of the interchanges and the block structure of D
!>          as determined by CHETRF_ROOK.
!>
```

*WORK*

```
!>          WORK is COMPLEX array, dimension (N)
!>
```

*INFO*

```
!>          INFO is INTEGER
!>          = 0: successful exit
!>          < 0: if INFO = -i, the i-th argument had an illegal value
!>          > 0: if INFO = i, D(i,i) = 0; the matrix is singular and its
!>               inverse could not be computed.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Contributors:**

```
!>
!>  November 2013,  Igor Kozachenko,
!>                  Computer Science Division,
!>                  University of California, Berkeley
!>
!>  September 2007, Sven Hammarling, Nicholas J. Higham, Craig Lucas,
!>                  School of Mathematics,
!>                  University of Manchester
!>
```

Definition at line **127** of file **chetri\_rook.f**.

## Author

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