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Diffstat (limited to '2.3-1/src/fortran/lapack/dtrti2.f')
| -rw-r--r-- | 2.3-1/src/fortran/lapack/dtrti2.f | 146 |
1 files changed, 146 insertions, 0 deletions
diff --git a/2.3-1/src/fortran/lapack/dtrti2.f b/2.3-1/src/fortran/lapack/dtrti2.f new file mode 100644 index 00000000..e7ae764d --- /dev/null +++ b/2.3-1/src/fortran/lapack/dtrti2.f @@ -0,0 +1,146 @@ + SUBROUTINE DTRTI2( UPLO, DIAG, N, A, LDA, INFO ) +* +* -- LAPACK routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + CHARACTER DIAG, UPLO + INTEGER INFO, LDA, N +* .. +* .. Array Arguments .. + DOUBLE PRECISION A( LDA, * ) +* .. +* +* Purpose +* ======= +* +* DTRTI2 computes the inverse of a real upper or lower triangular +* matrix. +* +* This is the Level 2 BLAS version of the algorithm. +* +* Arguments +* ========= +* +* UPLO (input) CHARACTER*1 +* Specifies whether the matrix A is upper or lower triangular. +* = 'U': Upper triangular +* = 'L': Lower triangular +* +* DIAG (input) CHARACTER*1 +* Specifies whether or not the matrix A is unit triangular. +* = 'N': Non-unit triangular +* = 'U': Unit triangular +* +* N (input) INTEGER +* The order of the matrix A. N >= 0. +* +* A (input/output) DOUBLE PRECISION array, dimension (LDA,N) +* On entry, the triangular matrix A. If UPLO = 'U', the +* leading n by n upper triangular part of the array A contains +* the upper triangular matrix, and the strictly lower +* triangular part of A is not referenced. If UPLO = 'L', the +* leading n by n lower triangular part of the array A contains +* the lower triangular matrix, and the strictly upper +* triangular part of A is not referenced. If DIAG = 'U', the +* diagonal elements of A are also not referenced and are +* assumed to be 1. +* +* On exit, the (triangular) inverse of the original matrix, in +* the same storage format. +* +* LDA (input) INTEGER +* The leading dimension of the array A. LDA >= max(1,N). +* +* INFO (output) INTEGER +* = 0: successful exit +* < 0: if INFO = -k, the k-th argument had an illegal value +* +* ===================================================================== +* +* .. Parameters .. + DOUBLE PRECISION ONE + PARAMETER ( ONE = 1.0D+0 ) +* .. +* .. Local Scalars .. + LOGICAL NOUNIT, UPPER + INTEGER J + DOUBLE PRECISION AJJ +* .. +* .. External Functions .. + LOGICAL LSAME + EXTERNAL LSAME +* .. +* .. External Subroutines .. + EXTERNAL DSCAL, DTRMV, XERBLA +* .. +* .. Intrinsic Functions .. + INTRINSIC MAX +* .. +* .. Executable Statements .. +* +* Test the input parameters. +* + INFO = 0 + UPPER = LSAME( UPLO, 'U' ) + NOUNIT = LSAME( DIAG, 'N' ) + IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN + INFO = -1 + ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN + INFO = -2 + ELSE IF( N.LT.0 ) THEN + INFO = -3 + ELSE IF( LDA.LT.MAX( 1, N ) ) THEN + INFO = -5 + END IF + IF( INFO.NE.0 ) THEN + CALL XERBLA( 'DTRTI2', -INFO ) + RETURN + END IF +* + IF( UPPER ) THEN +* +* Compute inverse of upper triangular matrix. +* + DO 10 J = 1, N + IF( NOUNIT ) THEN + A( J, J ) = ONE / A( J, J ) + AJJ = -A( J, J ) + ELSE + AJJ = -ONE + END IF +* +* Compute elements 1:j-1 of j-th column. +* + CALL DTRMV( 'Upper', 'No transpose', DIAG, J-1, A, LDA, + $ A( 1, J ), 1 ) + CALL DSCAL( J-1, AJJ, A( 1, J ), 1 ) + 10 CONTINUE + ELSE +* +* Compute inverse of lower triangular matrix. +* + DO 20 J = N, 1, -1 + IF( NOUNIT ) THEN + A( J, J ) = ONE / A( J, J ) + AJJ = -A( J, J ) + ELSE + AJJ = -ONE + END IF + IF( J.LT.N ) THEN +* +* Compute elements j+1:n of j-th column. +* + CALL DTRMV( 'Lower', 'No transpose', DIAG, N-J, + $ A( J+1, J+1 ), LDA, A( J+1, J ), 1 ) + CALL DSCAL( N-J, AJJ, A( J+1, J ), 1 ) + END IF + 20 CONTINUE + END IF +* + RETURN +* +* End of DTRTI2 +* + END |