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Diffstat (limited to 'src/fortran/lapack/dtrtri.f')
| -rw-r--r-- | src/fortran/lapack/dtrtri.f | 176 |
1 files changed, 176 insertions, 0 deletions
diff --git a/src/fortran/lapack/dtrtri.f b/src/fortran/lapack/dtrtri.f new file mode 100644 index 0000000..375813c --- /dev/null +++ b/src/fortran/lapack/dtrtri.f @@ -0,0 +1,176 @@ + SUBROUTINE DTRTRI( 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 +* ======= +* +* DTRTRI computes the inverse of a real upper or lower triangular +* matrix A. +* +* This is the Level 3 BLAS version of the algorithm. +* +* Arguments +* ========= +* +* UPLO (input) CHARACTER*1 +* = 'U': A is upper triangular; +* = 'L': A is lower triangular. +* +* DIAG (input) CHARACTER*1 +* = 'N': A is non-unit triangular; +* = 'U': A is 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 = -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. +* +* ===================================================================== +* +* .. Parameters .. + DOUBLE PRECISION ONE, ZERO + PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 ) +* .. +* .. Local Scalars .. + LOGICAL NOUNIT, UPPER + INTEGER J, JB, NB, NN +* .. +* .. External Functions .. + LOGICAL LSAME + INTEGER ILAENV + EXTERNAL LSAME, ILAENV +* .. +* .. External Subroutines .. + EXTERNAL DTRMM, DTRSM, DTRTI2, XERBLA +* .. +* .. Intrinsic Functions .. + INTRINSIC MAX, MIN +* .. +* .. 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( 'DTRTRI', -INFO ) + RETURN + END IF +* +* Quick return if possible +* + IF( N.EQ.0 ) + $ RETURN +* +* Check for singularity if non-unit. +* + IF( NOUNIT ) THEN + DO 10 INFO = 1, N + IF( A( INFO, INFO ).EQ.ZERO ) + $ RETURN + 10 CONTINUE + INFO = 0 + END IF +* +* Determine the block size for this environment. +* + NB = ILAENV( 1, 'DTRTRI', UPLO // DIAG, N, -1, -1, -1 ) + IF( NB.LE.1 .OR. NB.GE.N ) THEN +* +* Use unblocked code +* + CALL DTRTI2( UPLO, DIAG, N, A, LDA, INFO ) + ELSE +* +* Use blocked code +* + IF( UPPER ) THEN +* +* Compute inverse of upper triangular matrix +* + DO 20 J = 1, N, NB + JB = MIN( NB, N-J+1 ) +* +* Compute rows 1:j-1 of current block column +* + CALL DTRMM( 'Left', 'Upper', 'No transpose', DIAG, J-1, + $ JB, ONE, A, LDA, A( 1, J ), LDA ) + CALL DTRSM( 'Right', 'Upper', 'No transpose', DIAG, J-1, + $ JB, -ONE, A( J, J ), LDA, A( 1, J ), LDA ) +* +* Compute inverse of current diagonal block +* + CALL DTRTI2( 'Upper', DIAG, JB, A( J, J ), LDA, INFO ) + 20 CONTINUE + ELSE +* +* Compute inverse of lower triangular matrix +* + NN = ( ( N-1 ) / NB )*NB + 1 + DO 30 J = NN, 1, -NB + JB = MIN( NB, N-J+1 ) + IF( J+JB.LE.N ) THEN +* +* Compute rows j+jb:n of current block column +* + CALL DTRMM( 'Left', 'Lower', 'No transpose', DIAG, + $ N-J-JB+1, JB, ONE, A( J+JB, J+JB ), LDA, + $ A( J+JB, J ), LDA ) + CALL DTRSM( 'Right', 'Lower', 'No transpose', DIAG, + $ N-J-JB+1, JB, -ONE, A( J, J ), LDA, + $ A( J+JB, J ), LDA ) + END IF +* +* Compute inverse of current diagonal block +* + CALL DTRTI2( 'Lower', DIAG, JB, A( J, J ), LDA, INFO ) + 30 CONTINUE + END IF + END IF +* + RETURN +* +* End of DTRTRI +* + END |