• NAME
• SYNOPSIS
• F95 INTERFACE
• C INTERFACE
• PURPOSE
• ARGUMENTS

NAME

spptri - compute 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, A, INFO)
  CHARACTER * 1 UPLO
  INTEGER N, INFO
  REAL A(*)

  SUBROUTINE SPPTRI_64( UPLO, N, A, INFO)
  CHARACTER * 1 UPLO
  INTEGER*8 N, INFO
  REAL A(*)

F95 INTERFACE

  SUBROUTINE PPTRI( UPLO, N, A, [INFO])
  CHARACTER(LEN=1) :: UPLO
  INTEGER :: N, INFO
  REAL, DIMENSION(:) :: A

  SUBROUTINE PPTRI_64( UPLO, N, A, [INFO])
  CHARACTER(LEN=1) :: UPLO
  INTEGER(8) :: N, INFO
  REAL, DIMENSION(:) :: A

C INTERFACE

#include <sunperf.h>

void spptri(char uplo, int n, float *a, int *info);

void spptri_64(char uplo, long n, float *a, long *info);

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)
  

   = 'U':  Upper triangular factor is stored in A;

   = 'L':  Lower triangular factor is stored in A.

• N (input)
  The order of the matrix A. N > = 0.

• A (input/output)
  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 A as follows: if UPLO = 'U', A(i + (j-1)*j/2) = U(i,j) for 1 < =i < =j; if UPLO = 'L', A(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)
  

   = 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.