# chetri2.f man page

chetri2.f —

## Synopsis

### Functions/Subroutines

subroutinechetri2(UPLO, N, A, LDA, IPIV, WORK, LWORK, INFO)CHETRI2

## Function/Subroutine Documentation

### subroutine chetri2 (characterUPLO, integerN, complex, dimension( lda, * )A, integerLDA, integer, dimension( * )IPIV, complex, dimension( * )WORK, integerLWORK, integerINFO)

**CHETRI2**

**Purpose:**

```
CHETRI2 computes the inverse of a COMPLEX hermitian indefinite matrix
A using the factorization A = U*D*U**T or A = L*D*L**T computed by
CHETRF. CHETRI2 set the LEADING DIMENSION of the workspace
before calling CHETRI2X that actually computes the inverse.
```

**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**T;
= 'L': Lower triangular, form is A = L*D*L**T.
```

*N*

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

*A*

```
A is COMPLEX array, dimension (LDA,N)
On entry, the NB diagonal matrix D and the multipliers
used to obtain the factor U or L as computed by CHETRF.
On exit, if INFO = 0, the (symmetric) 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 NB structure of D
as determined by CHETRF.
```

*WORK*

`WORK is COMPLEX array, dimension (N+NB+1)*(NB+3)`

*LWORK*

```
LWORK is INTEGER
The dimension of the array WORK.
WORK is size >= (N+NB+1)*(NB+3)
If LDWORK = -1, then a workspace query is assumed; the routine
calculates:
- the optimal size of the WORK array, returns
this value as the first entry of the WORK array,
- and no error message related to LDWORK is issued by XERBLA.
```

*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.

**Date:**

November 2011

Definition at line 128 of file chetri2.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

chetri2(3) is an alias of chetri2.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK