---
name: "dsptri"
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/dsptri.f"
---

# dsptri(3)

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

## NAME

SRC/dsptri.f

## SYNOPSIS

### Functions/Subroutines

subroutine **dsptri** (uplo, n, ap, ipiv, work, info)\
 **DSPTRI**

## Function/Subroutine Documentation

### subroutine dsptri (character uplo, integer n, double precision, dimension( \* ) ap, integer, dimension( \* ) ipiv, double precision, dimension( \* ) work, integer info)

**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.

Definition at line **108** of file **dsptri.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.