---
name: "spptri"
section: "3lapack"
platform: "linux"
package: "liblapack-doc"
version: "3.2.1-8"
release: "Debian 6.0 (Squeeze)"
platforms: ["linux"]
url: "https://new.carta.tech/spptri/3lapack"
---

# spptri(3lapack)

computes the inverse of a real symmetric positive definite matrix A using the Cholesky factorization A = U\*\*T\*U or A = L\*L\*\*T computed by SPPTRF

## NAME

SPPTRI - computes the inverse of a real symmetric positive definite matrix A using the Cholesky factorization A = U\*\*T\*U or A = L\*L\*\*T computed by SPPTRF

## SYNOPSIS

- SUBROUTINE SPPTRI(

  UPLO, N, AP, INFO )

- CHARACTER

  UPLO

- INTEGER

  INFO, N

- REAL

  AP( \* )

## PURPOSE

SPPTRI computes the inverse of a real symmetric positive definite matrix A using the Cholesky factorization A = U\*\*T\*U or A = L\*L\*\*T computed by SPPTRF.

## ARGUMENTS

- UPLO (input) CHARACTER\*1

  \= 'U':  Upper triangular factor is stored in AP;\
   \= 'L':  Lower triangular factor is stored in AP.

- N (input) INTEGER

  The order of the matrix A.  N \>= 0.

- AP (input/output) REAL array, dimension (N\*(N+1)/2)

  On entry, the triangular factor U or L from the Cholesky factorization A = U\*\*T\*U or A = L\*L\*\*T, packed columnwise as a linear array.  The j-th column of U or L is stored in the array AP as follows: if UPLO = 'U', AP(i + (j-1)\*j/2) = U(i,j) for 1\<=i\<=j; if UPLO = 'L', AP(i + (j-1)\*(2n-j)/2) = L(i,j) for j\<=i\<=n. On exit, the upper or lower triangle of the (symmetric) inverse of A, overwriting the input factor U or L.

- INFO (output) INTEGER

  \= 0:  successful exit\
   \< 0:  if INFO = -i, the i-th argument had an illegal value\
   \> 0:  if INFO = i, the (i,i) element of the factor U or L is zero, and the inverse could not be computed.