Annotation of rpl/lapack/lapack/dtrti2.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE DTRTI2( UPLO, DIAG, N, A, LDA, INFO )
! 2: *
! 3: * -- LAPACK routine (version 3.2) --
! 4: * -- LAPACK is a software package provided by Univ. of Tennessee, --
! 5: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
! 6: * November 2006
! 7: *
! 8: * .. Scalar Arguments ..
! 9: CHARACTER DIAG, UPLO
! 10: INTEGER INFO, LDA, N
! 11: * ..
! 12: * .. Array Arguments ..
! 13: DOUBLE PRECISION A( LDA, * )
! 14: * ..
! 15: *
! 16: * Purpose
! 17: * =======
! 18: *
! 19: * DTRTI2 computes the inverse of a real upper or lower triangular
! 20: * matrix.
! 21: *
! 22: * This is the Level 2 BLAS version of the algorithm.
! 23: *
! 24: * Arguments
! 25: * =========
! 26: *
! 27: * UPLO (input) CHARACTER*1
! 28: * Specifies whether the matrix A is upper or lower triangular.
! 29: * = 'U': Upper triangular
! 30: * = 'L': Lower triangular
! 31: *
! 32: * DIAG (input) CHARACTER*1
! 33: * Specifies whether or not the matrix A is unit triangular.
! 34: * = 'N': Non-unit triangular
! 35: * = 'U': Unit triangular
! 36: *
! 37: * N (input) INTEGER
! 38: * The order of the matrix A. N >= 0.
! 39: *
! 40: * A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
! 41: * On entry, the triangular matrix A. If UPLO = 'U', the
! 42: * leading n by n upper triangular part of the array A contains
! 43: * the upper triangular matrix, and the strictly lower
! 44: * triangular part of A is not referenced. If UPLO = 'L', the
! 45: * leading n by n lower triangular part of the array A contains
! 46: * the lower triangular matrix, and the strictly upper
! 47: * triangular part of A is not referenced. If DIAG = 'U', the
! 48: * diagonal elements of A are also not referenced and are
! 49: * assumed to be 1.
! 50: *
! 51: * On exit, the (triangular) inverse of the original matrix, in
! 52: * the same storage format.
! 53: *
! 54: * LDA (input) INTEGER
! 55: * The leading dimension of the array A. LDA >= max(1,N).
! 56: *
! 57: * INFO (output) INTEGER
! 58: * = 0: successful exit
! 59: * < 0: if INFO = -k, the k-th argument had an illegal value
! 60: *
! 61: * =====================================================================
! 62: *
! 63: * .. Parameters ..
! 64: DOUBLE PRECISION ONE
! 65: PARAMETER ( ONE = 1.0D+0 )
! 66: * ..
! 67: * .. Local Scalars ..
! 68: LOGICAL NOUNIT, UPPER
! 69: INTEGER J
! 70: DOUBLE PRECISION AJJ
! 71: * ..
! 72: * .. External Functions ..
! 73: LOGICAL LSAME
! 74: EXTERNAL LSAME
! 75: * ..
! 76: * .. External Subroutines ..
! 77: EXTERNAL DSCAL, DTRMV, XERBLA
! 78: * ..
! 79: * .. Intrinsic Functions ..
! 80: INTRINSIC MAX
! 81: * ..
! 82: * .. Executable Statements ..
! 83: *
! 84: * Test the input parameters.
! 85: *
! 86: INFO = 0
! 87: UPPER = LSAME( UPLO, 'U' )
! 88: NOUNIT = LSAME( DIAG, 'N' )
! 89: IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
! 90: INFO = -1
! 91: ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
! 92: INFO = -2
! 93: ELSE IF( N.LT.0 ) THEN
! 94: INFO = -3
! 95: ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
! 96: INFO = -5
! 97: END IF
! 98: IF( INFO.NE.0 ) THEN
! 99: CALL XERBLA( 'DTRTI2', -INFO )
! 100: RETURN
! 101: END IF
! 102: *
! 103: IF( UPPER ) THEN
! 104: *
! 105: * Compute inverse of upper triangular matrix.
! 106: *
! 107: DO 10 J = 1, N
! 108: IF( NOUNIT ) THEN
! 109: A( J, J ) = ONE / A( J, J )
! 110: AJJ = -A( J, J )
! 111: ELSE
! 112: AJJ = -ONE
! 113: END IF
! 114: *
! 115: * Compute elements 1:j-1 of j-th column.
! 116: *
! 117: CALL DTRMV( 'Upper', 'No transpose', DIAG, J-1, A, LDA,
! 118: $ A( 1, J ), 1 )
! 119: CALL DSCAL( J-1, AJJ, A( 1, J ), 1 )
! 120: 10 CONTINUE
! 121: ELSE
! 122: *
! 123: * Compute inverse of lower triangular matrix.
! 124: *
! 125: DO 20 J = N, 1, -1
! 126: IF( NOUNIT ) THEN
! 127: A( J, J ) = ONE / A( J, J )
! 128: AJJ = -A( J, J )
! 129: ELSE
! 130: AJJ = -ONE
! 131: END IF
! 132: IF( J.LT.N ) THEN
! 133: *
! 134: * Compute elements j+1:n of j-th column.
! 135: *
! 136: CALL DTRMV( 'Lower', 'No transpose', DIAG, N-J,
! 137: $ A( J+1, J+1 ), LDA, A( J+1, J ), 1 )
! 138: CALL DSCAL( N-J, AJJ, A( J+1, J ), 1 )
! 139: END IF
! 140: 20 CONTINUE
! 141: END IF
! 142: *
! 143: RETURN
! 144: *
! 145: * End of DTRTI2
! 146: *
! 147: END
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