# dsptri.f man page

dsptri.f —

## Synopsis

### Functions/Subroutines

subroutinedsptri(UPLO, N, AP, IPIV, WORK, INFO)DSPTRI

## Function/Subroutine Documentation

### subroutine dsptri (characterUPLO, integerN, double precision, dimension( * )AP, integer, dimension( * )IPIV, double precision, dimension( * )WORK, integerINFO)

**DSPTRI**

**Purpose:**

```
DSPTRI computes the inverse of a real symmetric indefinite matrix
A in packed storage using the factorization A = U*D*U**T or
A = L*D*L**T computed by DSPTRF.
```

**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.
```

*AP*

```
AP is DOUBLE PRECISION array, dimension (N*(N+1)/2)
On entry, the block diagonal matrix D and the multipliers
used to obtain the factor U or L as computed by DSPTRF,
stored as a packed triangular matrix.
On exit, if INFO = 0, the (symmetric) inverse of the original
matrix, stored as a packed triangular matrix. The j-th column
of inv(A) is stored in the array AP as follows:
if UPLO = 'U', AP(i + (j-1)*j/2) = inv(A)(i,j) for 1<=i<=j;
if UPLO = 'L',
AP(i + (j-1)*(2n-j)/2) = inv(A)(i,j) for j<=i<=n.
```

*IPIV*

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

*WORK*

`WORK is DOUBLE PRECISION 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.

**Date:**

November 2011

Definition at line 110 of file dsptri.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

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

Sat Nov 16 2013 Version 3.4.2 LAPACK