Julie
bc6a755be4
This is really old school, but a lot of times we have users sending us copy pasting of codes, and that is the only way to know the version of the code.
191 lines
5.0 KiB
FortranFixed
191 lines
5.0 KiB
FortranFixed
*> \brief \b CPPTRI
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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*> \htmlonly
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*> Download CPPTRI + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/cpptri.f">
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*> [TGZ]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/cpptri.f">
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*> [ZIP]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/cpptri.f">
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*> [TXT]</a>
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*> \endhtmlonly
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*
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* Definition:
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* ===========
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*
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* SUBROUTINE CPPTRI( UPLO, N, AP, INFO )
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*
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* .. Scalar Arguments ..
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* CHARACTER UPLO
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* INTEGER INFO, N
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* ..
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* .. Array Arguments ..
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* COMPLEX AP( * )
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* ..
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*> CPPTRI computes the inverse of a complex Hermitian positive definite
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*> matrix A using the Cholesky factorization A = U**H*U or A = L*L**H
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*> computed by CPPTRF.
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in] UPLO
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*> \verbatim
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*> UPLO is CHARACTER*1
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*> = 'U': Upper triangular factor is stored in AP;
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*> = 'L': Lower triangular factor is stored in AP.
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*> \endverbatim
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*>
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*> \param[in] N
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*> \verbatim
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*> N is INTEGER
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*> The order of the matrix A. N >= 0.
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*> \endverbatim
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*>
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*> \param[in,out] AP
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*> \verbatim
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*> AP is COMPLEX array, dimension (N*(N+1)/2)
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*> On entry, the triangular factor U or L from the Cholesky
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*> factorization A = U**H*U or A = L*L**H, packed columnwise as
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*> a linear array. The j-th column of U or L is stored in the
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*> array AP as follows:
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*> if UPLO = 'U', AP(i + (j-1)*j/2) = U(i,j) for 1<=i<=j;
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*> if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = L(i,j) for j<=i<=n.
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*>
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*> On exit, the upper or lower triangle of the (Hermitian)
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*> inverse of A, overwriting the input factor U or L.
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*> \endverbatim
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*>
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*> \param[out] INFO
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*> \verbatim
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*> INFO is INTEGER
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*> = 0: successful exit
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*> < 0: if INFO = -i, the i-th argument had an illegal value
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*> > 0: if INFO = i, the (i,i) element of the factor U or L is
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*> zero, and the inverse could not be computed.
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \author NAG Ltd.
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*
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*> \date December 2016
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*
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*> \ingroup complexOTHERcomputational
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*
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* =====================================================================
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SUBROUTINE CPPTRI( UPLO, N, AP, INFO )
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*
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* -- LAPACK computational routine (version 3.7.0) --
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* -- LAPACK is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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* December 2016
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*
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* .. Scalar Arguments ..
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CHARACTER UPLO
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INTEGER INFO, N
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* ..
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* .. Array Arguments ..
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COMPLEX AP( * )
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* ..
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*
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* =====================================================================
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*
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* .. Parameters ..
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REAL ONE
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PARAMETER ( ONE = 1.0E+0 )
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* ..
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* .. Local Scalars ..
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LOGICAL UPPER
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INTEGER J, JC, JJ, JJN
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REAL AJJ
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* ..
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* .. External Functions ..
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LOGICAL LSAME
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COMPLEX CDOTC
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EXTERNAL LSAME, CDOTC
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* ..
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* .. External Subroutines ..
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EXTERNAL CHPR, CSSCAL, CTPMV, CTPTRI, XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC REAL
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* ..
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* .. Executable Statements ..
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*
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* Test the input parameters.
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*
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INFO = 0
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UPPER = LSAME( UPLO, 'U' )
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IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
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INFO = -1
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ELSE IF( N.LT.0 ) THEN
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INFO = -2
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END IF
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IF( INFO.NE.0 ) THEN
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CALL XERBLA( 'CPPTRI', -INFO )
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RETURN
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END IF
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*
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* Quick return if possible
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*
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IF( N.EQ.0 )
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$ RETURN
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*
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* Invert the triangular Cholesky factor U or L.
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*
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CALL CTPTRI( UPLO, 'Non-unit', N, AP, INFO )
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IF( INFO.GT.0 )
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$ RETURN
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IF( UPPER ) THEN
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*
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* Compute the product inv(U) * inv(U)**H.
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*
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JJ = 0
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DO 10 J = 1, N
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JC = JJ + 1
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JJ = JJ + J
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IF( J.GT.1 )
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$ CALL CHPR( 'Upper', J-1, ONE, AP( JC ), 1, AP )
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AJJ = AP( JJ )
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CALL CSSCAL( J, AJJ, AP( JC ), 1 )
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10 CONTINUE
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*
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ELSE
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*
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* Compute the product inv(L)**H * inv(L).
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*
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JJ = 1
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DO 20 J = 1, N
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JJN = JJ + N - J + 1
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AP( JJ ) = REAL( CDOTC( N-J+1, AP( JJ ), 1, AP( JJ ), 1 ) )
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IF( J.LT.N )
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$ CALL CTPMV( 'Lower', 'Conjugate transpose', 'Non-unit',
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$ N-J, AP( JJN ), AP( JJ+1 ), 1 )
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JJ = JJN
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20 CONTINUE
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END IF
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*
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RETURN
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*
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* End of CPPTRI
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*
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END
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