LAPACK  3.4.2
LAPACK: Linear Algebra PACKage
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stptri.f File Reference

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Functions/Subroutines

subroutine stptri (UPLO, DIAG, N, AP, INFO)
 STPTRI

Function/Subroutine Documentation

subroutine stptri ( character  UPLO,
character  DIAG,
integer  N,
real, dimension( * )  AP,
integer  INFO 
)

STPTRI

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Purpose: 
 STPTRI computes the inverse of a real upper or lower triangular
 matrix A stored in packed format.
Parameters:
[in]UPLO
          UPLO is CHARACTER*1
          = 'U':  A is upper triangular;
          = 'L':  A is lower triangular.
[in]DIAG
          DIAG is CHARACTER*1
          = 'N':  A is non-unit triangular;
          = 'U':  A is unit triangular.
[in]N
          N is INTEGER
          The order of the matrix A.  N >= 0.
[in,out]AP
          AP is REAL array, dimension (N*(N+1)/2)
          On entry, the upper or lower triangular matrix A, stored
          columnwise in a linear array.  The j-th column of A is stored
          in the array AP as follows:
          if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
          if UPLO = 'L', AP(i + (j-1)*((2*n-j)/2) = A(i,j) for j<=i<=n.
          See below for further details.
          On exit, the (triangular) inverse of the original matrix, in
          the same packed storage format.
[out]INFO
          INFO is INTEGER
          = 0:  successful exit
          < 0:  if INFO = -i, the i-th argument had an illegal value
          > 0:  if INFO = i, A(i,i) is exactly zero.  The triangular
                matrix is singular and its inverse can not be computed.
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
November 2011
Further Details: 
  A triangular matrix A can be transferred to packed storage using one
  of the following program segments:

  UPLO = 'U':                      UPLO = 'L':

        JC = 1                           JC = 1
        DO 2 J = 1, N                    DO 2 J = 1, N
           DO 1 I = 1, J                    DO 1 I = J, N
              AP(JC+I-1) = A(I,J)              AP(JC+I-J) = A(I,J)
      1    CONTINUE                    1    CONTINUE
           JC = JC + J                      JC = JC + N - J + 1
      2 CONTINUE                       2 CONTINUE

Definition at line 118 of file stptri.f.

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