| SUBROUTINE STRTRIF( UPLO, DIAG, N, A, LDA, INFO ) |
| * |
| * -- LAPACK routine (version 3.0) -- |
| * Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd., |
| * Courant Institute, Argonne National Lab, and Rice University |
| * March 31, 1993 |
| * |
| * .. Scalar Arguments .. |
| CHARACTER DIAG, UPLO |
| INTEGER INFO, LDA, N |
| * .. |
| * .. Array Arguments .. |
| REAL A( LDA, * ) |
| * .. |
| * |
| * Purpose |
| * ======= |
| * |
| * STRTRI 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) REAL 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 .. |
| REAL ONE, ZERO |
| PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 ) |
| * .. |
| * .. Local Scalars .. |
| LOGICAL NOUNIT, UPPER |
| INTEGER J, JB, NB, NN |
| * .. |
| * .. External Functions .. |
| LOGICAL LSAME |
| EXTERNAL LSAME |
| * .. |
| * .. External Subroutines .. |
| EXTERNAL STRMM, STRSM, STRTI2, 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( 'STRTRI', -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 = 128 |
| IF( NB.LE.1 .OR. NB.GE.N ) THEN |
| * |
| * Use unblocked code |
| * |
| CALL STRTI2( 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 STRMM( 'Left', 'Upper', 'No transpose', DIAG, J-1, |
| $ JB, ONE, A, LDA, A( 1, J ), LDA ) |
| CALL STRSM( 'Right', 'Upper', 'No transpose', DIAG, J-1, |
| $ JB, -ONE, A( J, J ), LDA, A( 1, J ), LDA ) |
| * |
| * Compute inverse of current diagonal block |
| * |
| CALL STRTI2( '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 STRMM( 'Left', 'Lower', 'No transpose', DIAG, |
| $ N-J-JB+1, JB, ONE, A( J+JB, J+JB ), LDA, |
| $ A( J+JB, J ), LDA ) |
| CALL STRSM( '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 STRTI2( 'Lower', DIAG, JB, A( J, J ), LDA, INFO ) |
| 30 CONTINUE |
| END IF |
| END IF |
| * |
| RETURN |
| * |
| * End of STRTRI |
| * |
| END |
