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 non-unit 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 j-th column of A is stored in the array AP as follows: if UPLO = aqUaq, AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j; if UPLO = aqLaq, 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.
- INFO (output) 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.
FURTHER DETAILS
A triangular matrix A can be transferred to packed storage using one of the following program segments:UPLO = aqUaq: UPLO = aqLaq:
JC
DO 2 J