Contents
dtptri - compute the inverse of a real upper or lower tri-
angular matrix A stored in packed format
SUBROUTINE DTPTRI(UPLO, DIAG, N, A, INFO)
CHARACTER * 1 UPLO, DIAG
INTEGER N, INFO
DOUBLE PRECISION A(*)
SUBROUTINE DTPTRI_64(UPLO, DIAG, N, A, INFO)
CHARACTER * 1 UPLO, DIAG
INTEGER*8 N, INFO
DOUBLE PRECISION A(*)
F95 INTERFACE
SUBROUTINE TPTRI(UPLO, DIAG, [N], A, [INFO])
CHARACTER(LEN=1) :: UPLO, DIAG
INTEGER :: N, INFO
REAL(8), DIMENSION(:) :: A
SUBROUTINE TPTRI_64(UPLO, DIAG, [N], A, [INFO])
CHARACTER(LEN=1) :: UPLO, DIAG
INTEGER(8) :: N, INFO
REAL(8), DIMENSION(:) :: A
C INTERFACE
#include <sunperf.h>
void dtptri(char uplo, char diag, int n, double *a, int
*info);
void dtptri_64(char uplo, char diag, long n, double *a, long
*info);
dtptri computes the inverse of a real upper or lower tri-
angular matrix A stored in packed format.
UPLO (input)
= 'U': A is upper triangular;
= 'L': A is lower triangular.
DIAG (input)
= 'N': A is non-unit triangular;
= 'U': A is unit triangular.
N (input) The order of the matrix A. N >= 0.
A (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 A as follows:
if UPLO = 'U', A(i + (j-1)*j/2) = A(i,j) for
1<=i<=j; if UPLO = 'L', A(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 for-
mat.
INFO (output)
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille-
gal value
> 0: if INFO = i, A(i,i) is exactly zero. The
triangular matrix is singular and its inverse can
not be computed.
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
A(JC+I-1) = A(I,J) A(JC+I-J) =
A(I,J)
1 CONTINUE 1 CONTINUE
JC = JC + J JC = JC + N - J +
1
2 CONTINUE 2 CONTINUE