Annotation of rpl/lapack/lapack/zpptri.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE ZPPTRI( UPLO, N, AP, 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 UPLO
! 10: INTEGER INFO, N
! 11: * ..
! 12: * .. Array Arguments ..
! 13: COMPLEX*16 AP( * )
! 14: * ..
! 15: *
! 16: * Purpose
! 17: * =======
! 18: *
! 19: * ZPPTRI computes the inverse of a complex Hermitian positive definite
! 20: * matrix A using the Cholesky factorization A = U**H*U or A = L*L**H
! 21: * computed by ZPPTRF.
! 22: *
! 23: * Arguments
! 24: * =========
! 25: *
! 26: * UPLO (input) CHARACTER*1
! 27: * = 'U': Upper triangular factor is stored in AP;
! 28: * = 'L': Lower triangular factor is stored in AP.
! 29: *
! 30: * N (input) INTEGER
! 31: * The order of the matrix A. N >= 0.
! 32: *
! 33: * AP (input/output) COMPLEX*16 array, dimension (N*(N+1)/2)
! 34: * On entry, the triangular factor U or L from the Cholesky
! 35: * factorization A = U**H*U or A = L*L**H, packed columnwise as
! 36: * a linear array. The j-th column of U or L is stored in the
! 37: * array AP as follows:
! 38: * if UPLO = 'U', AP(i + (j-1)*j/2) = U(i,j) for 1<=i<=j;
! 39: * if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = L(i,j) for j<=i<=n.
! 40: *
! 41: * On exit, the upper or lower triangle of the (Hermitian)
! 42: * inverse of A, overwriting the input factor U or L.
! 43: *
! 44: * INFO (output) INTEGER
! 45: * = 0: successful exit
! 46: * < 0: if INFO = -i, the i-th argument had an illegal value
! 47: * > 0: if INFO = i, the (i,i) element of the factor U or L is
! 48: * zero, and the inverse could not be computed.
! 49: *
! 50: * =====================================================================
! 51: *
! 52: * .. Parameters ..
! 53: DOUBLE PRECISION ONE
! 54: PARAMETER ( ONE = 1.0D+0 )
! 55: * ..
! 56: * .. Local Scalars ..
! 57: LOGICAL UPPER
! 58: INTEGER J, JC, JJ, JJN
! 59: DOUBLE PRECISION AJJ
! 60: * ..
! 61: * .. External Functions ..
! 62: LOGICAL LSAME
! 63: COMPLEX*16 ZDOTC
! 64: EXTERNAL LSAME, ZDOTC
! 65: * ..
! 66: * .. External Subroutines ..
! 67: EXTERNAL XERBLA, ZDSCAL, ZHPR, ZTPMV, ZTPTRI
! 68: * ..
! 69: * .. Intrinsic Functions ..
! 70: INTRINSIC DBLE
! 71: * ..
! 72: * .. Executable Statements ..
! 73: *
! 74: * Test the input parameters.
! 75: *
! 76: INFO = 0
! 77: UPPER = LSAME( UPLO, 'U' )
! 78: IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
! 79: INFO = -1
! 80: ELSE IF( N.LT.0 ) THEN
! 81: INFO = -2
! 82: END IF
! 83: IF( INFO.NE.0 ) THEN
! 84: CALL XERBLA( 'ZPPTRI', -INFO )
! 85: RETURN
! 86: END IF
! 87: *
! 88: * Quick return if possible
! 89: *
! 90: IF( N.EQ.0 )
! 91: $ RETURN
! 92: *
! 93: * Invert the triangular Cholesky factor U or L.
! 94: *
! 95: CALL ZTPTRI( UPLO, 'Non-unit', N, AP, INFO )
! 96: IF( INFO.GT.0 )
! 97: $ RETURN
! 98: IF( UPPER ) THEN
! 99: *
! 100: * Compute the product inv(U) * inv(U)'.
! 101: *
! 102: JJ = 0
! 103: DO 10 J = 1, N
! 104: JC = JJ + 1
! 105: JJ = JJ + J
! 106: IF( J.GT.1 )
! 107: $ CALL ZHPR( 'Upper', J-1, ONE, AP( JC ), 1, AP )
! 108: AJJ = AP( JJ )
! 109: CALL ZDSCAL( J, AJJ, AP( JC ), 1 )
! 110: 10 CONTINUE
! 111: *
! 112: ELSE
! 113: *
! 114: * Compute the product inv(L)' * inv(L).
! 115: *
! 116: JJ = 1
! 117: DO 20 J = 1, N
! 118: JJN = JJ + N - J + 1
! 119: AP( JJ ) = DBLE( ZDOTC( N-J+1, AP( JJ ), 1, AP( JJ ), 1 ) )
! 120: IF( J.LT.N )
! 121: $ CALL ZTPMV( 'Lower', 'Conjugate transpose', 'Non-unit',
! 122: $ N-J, AP( JJN ), AP( JJ+1 ), 1 )
! 123: JJ = JJN
! 124: 20 CONTINUE
! 125: END IF
! 126: *
! 127: RETURN
! 128: *
! 129: * End of ZPPTRI
! 130: *
! 131: END
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