97 lines
2.5 KiB
Fortran
97 lines
2.5 KiB
Fortran
SUBROUTINE SPOTRIF( UPLO, N, A, LDA, INFO )
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*
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* -- LAPACK routine (version 3.1) --
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* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
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* November 2006
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*
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* .. Scalar Arguments ..
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CHARACTER UPLO
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INTEGER INFO, LDA, N
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* ..
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* .. Array Arguments ..
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REAL A( LDA, * )
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* ..
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*
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* Purpose
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* =======
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*
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* SPOTRI computes the inverse of a real symmetric positive definite
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* matrix A using the Cholesky factorization A = U**T*U or A = L*L**T
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* computed by SPOTRF.
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*
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* Arguments
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* =========
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*
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* UPLO (input) CHARACTER*1
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* = 'U': Upper triangle of A is stored;
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* = 'L': Lower triangle of A is stored.
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*
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* N (input) INTEGER
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* The order of the matrix A. N >= 0.
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*
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* A (input/output) REAL array, dimension (LDA,N)
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* On entry, the triangular factor U or L from the Cholesky
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* factorization A = U**T*U or A = L*L**T, as computed by
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* SPOTRF.
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* On exit, the upper or lower triangle of the (symmetric)
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* inverse of A, overwriting the input factor U or L.
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*
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* LDA (input) INTEGER
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* The leading dimension of the array A. LDA >= max(1,N).
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*
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* INFO (output) 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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*
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* =====================================================================
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*
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* .. External Functions ..
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LOGICAL LSAME
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EXTERNAL LSAME
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* ..
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* .. External Subroutines ..
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EXTERNAL SLAUUM, STRTRI, XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC MAX
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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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IF( .NOT.LSAME( UPLO, 'U' ) .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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ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
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INFO = -4
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END IF
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IF( INFO.NE.0 ) THEN
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CALL XERBLA( 'SPOTRI', -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 STRTRI( UPLO, 'Non-unit', N, A, LDA, INFO )
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IF( INFO.GT.0 )
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$ RETURN
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*
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* Form inv(U)*inv(U)' or inv(L)'*inv(L).
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*
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CALL SLAUUM( UPLO, N, A, LDA, INFO )
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*
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RETURN
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*
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* End of SPOTRI
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*
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END
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