| SUBROUTINE CTRTI2F( 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 .. |
| COMPLEX A( LDA, * ) |
| * .. |
| * |
| * Purpose |
| * ======= |
| * |
| * CTRTI2 computes the inverse of a complex 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) COMPLEX 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 .. |
| COMPLEX ONE |
| PARAMETER ( ONE = ( 1.0E+0, 0.0E+0 ) ) |
| * .. |
| * .. Local Scalars .. |
| LOGICAL NOUNIT, UPPER |
| INTEGER J |
| COMPLEX AJJ |
| * .. |
| * .. External Functions .. |
| LOGICAL LSAME |
| EXTERNAL LSAME |
| * .. |
| * .. External Subroutines .. |
| EXTERNAL CSCAL, CTRMV, 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( 'CTRTI2', -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 CTRMV( 'Upper', 'No transpose', DIAG, J-1, A, LDA, |
| $ A( 1, J ), 1 ) |
| CALL CSCAL( 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 CTRMV( 'Lower', 'No transpose', DIAG, N-J, |
| $ A( J+1, J+1 ), LDA, A( J+1, J ), 1 ) |
| CALL CSCAL( N-J, AJJ, A( J+1, J ), 1 ) |
| END IF |
| 20 CONTINUE |
| END IF |
| * |
| RETURN |
| * |
| * End of CTRTI2 |
| * |
| END |
