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Diffstat (limited to 'src/fortran/lapack/zgetf2.f')
| -rw-r--r-- | src/fortran/lapack/zgetf2.f | 148 |
1 files changed, 148 insertions, 0 deletions
diff --git a/src/fortran/lapack/zgetf2.f b/src/fortran/lapack/zgetf2.f new file mode 100644 index 0000000..a2dc183 --- /dev/null +++ b/src/fortran/lapack/zgetf2.f @@ -0,0 +1,148 @@ + SUBROUTINE ZGETF2( M, N, A, LDA, IPIV, INFO ) +* +* -- LAPACK routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + INTEGER INFO, LDA, M, N +* .. +* .. Array Arguments .. + INTEGER IPIV( * ) + COMPLEX*16 A( LDA, * ) +* .. +* +* Purpose +* ======= +* +* ZGETF2 computes an LU factorization of a general m-by-n matrix A +* using partial pivoting with row interchanges. +* +* The factorization has the form +* A = P * L * U +* where P is a permutation matrix, L is lower triangular with unit +* diagonal elements (lower trapezoidal if m > n), and U is upper +* triangular (upper trapezoidal if m < n). +* +* This is the right-looking Level 2 BLAS version of the algorithm. +* +* Arguments +* ========= +* +* M (input) INTEGER +* The number of rows of the matrix A. M >= 0. +* +* N (input) INTEGER +* The number of columns of the matrix A. N >= 0. +* +* A (input/output) COMPLEX*16 array, dimension (LDA,N) +* On entry, the m by n matrix to be factored. +* On exit, the factors L and U from the factorization +* A = P*L*U; the unit diagonal elements of L are not stored. +* +* LDA (input) INTEGER +* The leading dimension of the array A. LDA >= max(1,M). +* +* IPIV (output) INTEGER array, dimension (min(M,N)) +* The pivot indices; for 1 <= i <= min(M,N), row i of the +* matrix was interchanged with row IPIV(i). +* +* INFO (output) INTEGER +* = 0: successful exit +* < 0: if INFO = -k, the k-th argument had an illegal value +* > 0: if INFO = k, U(k,k) is exactly zero. The factorization +* has been completed, but the factor U is exactly +* singular, and division by zero will occur if it is used +* to solve a system of equations. +* +* ===================================================================== +* +* .. Parameters .. + COMPLEX*16 ONE, ZERO + PARAMETER ( ONE = ( 1.0D+0, 0.0D+0 ), + $ ZERO = ( 0.0D+0, 0.0D+0 ) ) +* .. +* .. Local Scalars .. + DOUBLE PRECISION SFMIN + INTEGER I, J, JP +* .. +* .. External Functions .. + DOUBLE PRECISION DLAMCH + INTEGER IZAMAX + EXTERNAL DLAMCH, IZAMAX +* .. +* .. External Subroutines .. + EXTERNAL XERBLA, ZGERU, ZSCAL, ZSWAP +* .. +* .. Intrinsic Functions .. + INTRINSIC MAX, MIN +* .. +* .. Executable Statements .. +* +* Test the input parameters. +* + INFO = 0 + IF( M.LT.0 ) THEN + INFO = -1 + ELSE IF( N.LT.0 ) THEN + INFO = -2 + ELSE IF( LDA.LT.MAX( 1, M ) ) THEN + INFO = -4 + END IF + IF( INFO.NE.0 ) THEN + CALL XERBLA( 'ZGETF2', -INFO ) + RETURN + END IF +* +* Quick return if possible +* + IF( M.EQ.0 .OR. N.EQ.0 ) + $ RETURN +* +* Compute machine safe minimum +* + SFMIN = DLAMCH('S') +* + DO 10 J = 1, MIN( M, N ) +* +* Find pivot and test for singularity. +* + JP = J - 1 + IZAMAX( M-J+1, A( J, J ), 1 ) + IPIV( J ) = JP + IF( A( JP, J ).NE.ZERO ) THEN +* +* Apply the interchange to columns 1:N. +* + IF( JP.NE.J ) + $ CALL ZSWAP( N, A( J, 1 ), LDA, A( JP, 1 ), LDA ) +* +* Compute elements J+1:M of J-th column. +* + IF( J.LT.M ) THEN + IF( ABS(A( J, J )) .GE. SFMIN ) THEN + CALL ZSCAL( M-J, ONE / A( J, J ), A( J+1, J ), 1 ) + ELSE + DO 20 I = 1, M-J + A( J+I, J ) = A( J+I, J ) / A( J, J ) + 20 CONTINUE + END IF + END IF +* + ELSE IF( INFO.EQ.0 ) THEN +* + INFO = J + END IF +* + IF( J.LT.MIN( M, N ) ) THEN +* +* Update trailing submatrix. +* + CALL ZGERU( M-J, N-J, -ONE, A( J+1, J ), 1, A( J, J+1 ), + $ LDA, A( J+1, J+1 ), LDA ) + END IF + 10 CONTINUE + RETURN +* +* End of ZGETF2 +* + END |