dtptri (l)  Linux Manuals
dtptri: computes the inverse of a real upper or lower triangular matrix A stored in packed format
NAME
DTPTRI  computes the inverse of a real upper or lower triangular matrix A stored in packed formatSYNOPSIS
 SUBROUTINE DTPTRI(
 UPLO, DIAG, N, AP, INFO )
 CHARACTER DIAG, UPLO
 INTEGER INFO, N
 DOUBLE PRECISION AP( * )
PURPOSE
DTPTRI computes the inverse of a real upper or lower triangular matrix A stored in packed format.ARGUMENTS
 UPLO (input) CHARACTER*1

= aqUaq: A is upper triangular;
= aqLaq: A is lower triangular.  DIAG (input) CHARACTER*1

= aqNaq: A is nonunit triangular;
= aqUaq: A is unit triangular.  N (input) INTEGER
 The order of the matrix A. N >= 0.
 AP (input/output) DOUBLE PRECISION array, dimension (N*(N+1)/2)
 On entry, the upper or lower triangular matrix A, stored columnwise in a linear array. The jth column of A is stored in the array AP as follows: if UPLO = aqUaq, AP(i + (j1)*j/2) = A(i,j) for 1<=i<=j; if UPLO = aqLaq, AP(i + (j1)*((2*nj)/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.
 INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = i, the ith 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.
FURTHER DETAILS
A triangular matrix A can be transferred to packed storage using one of the following program segments:UPLO = aqUaq: UPLO = aqLaq:
JC
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