From 277d1edfa17bf3719d90ddbac8e31f6181e952c3 Mon Sep 17 00:00:00 2001 From: Sandeep Gupta Date: Sun, 18 Jun 2017 23:55:40 +0530 Subject: First commit --- src/fortran/lapack/dpotf2.f | 167 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 167 insertions(+) create mode 100644 src/fortran/lapack/dpotf2.f (limited to 'src/fortran/lapack/dpotf2.f') diff --git a/src/fortran/lapack/dpotf2.f b/src/fortran/lapack/dpotf2.f new file mode 100644 index 00000000..b7d65e91 --- /dev/null +++ b/src/fortran/lapack/dpotf2.f @@ -0,0 +1,167 @@ + SUBROUTINE DPOTF2( UPLO, N, A, LDA, INFO ) +* +* -- LAPACK routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + CHARACTER UPLO + INTEGER INFO, LDA, N +* .. +* .. Array Arguments .. + DOUBLE PRECISION A( LDA, * ) +* .. +* +* Purpose +* ======= +* +* DPOTF2 computes the Cholesky factorization of a real symmetric +* positive definite matrix A. +* +* The factorization has the form +* A = U' * U , if UPLO = 'U', or +* A = L * L', if UPLO = 'L', +* where U is an upper triangular matrix and L is lower triangular. +* +* This is the unblocked version of the algorithm, calling Level 2 BLAS. +* +* Arguments +* ========= +* +* UPLO (input) CHARACTER*1 +* Specifies whether the upper or lower triangular part of the +* symmetric matrix A is stored. +* = 'U': Upper triangular +* = 'L': Lower triangular +* +* N (input) INTEGER +* The order of the matrix A. N >= 0. +* +* A (input/output) DOUBLE PRECISION array, dimension (LDA,N) +* On entry, the symmetric matrix A. If UPLO = 'U', the leading +* n by n upper triangular part of A contains the upper +* triangular part of the matrix A, and the strictly lower +* triangular part of A is not referenced. If UPLO = 'L', the +* leading n by n lower triangular part of A contains the lower +* triangular part of the matrix A, and the strictly upper +* triangular part of A is not referenced. +* +* On exit, if INFO = 0, the factor U or L from the Cholesky +* factorization A = U'*U or A = L*L'. +* +* 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 +* > 0: if INFO = k, the leading minor of order k is not +* positive definite, and the factorization could not be +* completed. +* +* ===================================================================== +* +* .. Parameters .. + DOUBLE PRECISION ONE, ZERO + PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 ) +* .. +* .. Local Scalars .. + LOGICAL UPPER + INTEGER J + DOUBLE PRECISION AJJ +* .. +* .. External Functions .. + LOGICAL LSAME + DOUBLE PRECISION DDOT + EXTERNAL LSAME, DDOT +* .. +* .. External Subroutines .. + EXTERNAL DGEMV, DSCAL, XERBLA +* .. +* .. Intrinsic Functions .. + INTRINSIC MAX, SQRT +* .. +* .. Executable Statements .. +* +* Test the input parameters. +* + INFO = 0 + UPPER = LSAME( UPLO, 'U' ) + IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN + INFO = -1 + ELSE IF( N.LT.0 ) THEN + INFO = -2 + ELSE IF( LDA.LT.MAX( 1, N ) ) THEN + INFO = -4 + END IF + IF( INFO.NE.0 ) THEN + CALL XERBLA( 'DPOTF2', -INFO ) + RETURN + END IF +* +* Quick return if possible +* + IF( N.EQ.0 ) + $ RETURN +* + IF( UPPER ) THEN +* +* Compute the Cholesky factorization A = U'*U. +* + DO 10 J = 1, N +* +* Compute U(J,J) and test for non-positive-definiteness. +* + AJJ = A( J, J ) - DDOT( J-1, A( 1, J ), 1, A( 1, J ), 1 ) + IF( AJJ.LE.ZERO ) THEN + A( J, J ) = AJJ + GO TO 30 + END IF + AJJ = SQRT( AJJ ) + A( J, J ) = AJJ +* +* Compute elements J+1:N of row J. +* + IF( J.LT.N ) THEN + CALL DGEMV( 'Transpose', J-1, N-J, -ONE, A( 1, J+1 ), + $ LDA, A( 1, J ), 1, ONE, A( J, J+1 ), LDA ) + CALL DSCAL( N-J, ONE / AJJ, A( J, J+1 ), LDA ) + END IF + 10 CONTINUE + ELSE +* +* Compute the Cholesky factorization A = L*L'. +* + DO 20 J = 1, N +* +* Compute L(J,J) and test for non-positive-definiteness. +* + AJJ = A( J, J ) - DDOT( J-1, A( J, 1 ), LDA, A( J, 1 ), + $ LDA ) + IF( AJJ.LE.ZERO ) THEN + A( J, J ) = AJJ + GO TO 30 + END IF + AJJ = SQRT( AJJ ) + A( J, J ) = AJJ +* +* Compute elements J+1:N of column J. +* + IF( J.LT.N ) THEN + CALL DGEMV( 'No transpose', N-J, J-1, -ONE, A( J+1, 1 ), + $ LDA, A( J, 1 ), LDA, ONE, A( J+1, J ), 1 ) + CALL DSCAL( N-J, ONE / AJJ, A( J+1, J ), 1 ) + END IF + 20 CONTINUE + END IF + GO TO 40 +* + 30 CONTINUE + INFO = J +* + 40 CONTINUE + RETURN +* +* End of DPOTF2 +* + END -- cgit