📄 inverse.f
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ELSE JY = 1 - ( N - 1 )*INCY END IF IF( INCX.EQ.1 )THEN DO 20, J = 1, N IF( Y( JY ).NE.ZERO )THEN TEMP = ALPHA*Y( JY ) DO 10, I = 1, M A( I, J ) = A( I, J ) + X( I )*TEMP 10 CONTINUE END IF JY = JY + INCY 20 CONTINUE ELSE IF( INCX.GT.0 )THEN KX = 1 ELSE KX = 1 - ( M - 1 )*INCX END IF DO 40, J = 1, N IF( Y( JY ).NE.ZERO )THEN TEMP = ALPHA*Y( JY ) IX = KX DO 30, I = 1, M A( I, J ) = A( I, J ) + X( IX )*TEMP IX = IX + INCX 30 CONTINUE END IF JY = JY + INCY 40 CONTINUE END IF* RETURN** End of DGER .* END SUBROUTINE DGESV( N, NRHS, A, LDA, IPIV, B, LDB, INFO )** -- LAPACK driver routine (version 1.0) --* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,* Courant Institute, Argonne National Lab, and Rice University* February 29, 1992** .. Scalar Arguments .. INTEGER INFO, LDA, LDB, N, NRHS* ..* .. Array Arguments .. INTEGER IPIV( * ) DOUBLE PRECISION A( LDA, * ), B( LDB, * )* ..** Purpose* =======** DGESV computes the solution to a real system of linear equations* A * X = B,* where A is an N by N matrix and X and B are N by NRHS matrices.** The LU decomposition with partial pivoting and row interchanges is* used to factor A as* A = P * L * U,* where P is a permutation matrix, L is unit lower triangular, and U is* upper triangular. The factored form of A is then used to solve the* system of equations A * X = B.** Arguments* =========** N (input) INTEGER* The number of linear equations, i.e., the order of the* matrix A. N >= 0.** NRHS (input) INTEGER* The number of right hand sides, i.e., the number of columns* of the matrix B. NRHS >= 0.** A (input/output) DOUBLE PRECISION array, dimension (LDA,N)* On entry, the N by N matrix of coefficients A.* 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,N).** IPIV (output) INTEGER array, dimension (N)* The pivot indices that define the permutation matrix P;* row i of the matrix was interchanged with row IPIV(i).** B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)* On entry, the N by NRHS matrix of right hand side vectors B* for the system of equations A*X = B.* On exit, if INFO = 0, the N by NRHS matrix of solution* vectors X.** LDB (input) INTEGER* The leading dimension of the array B. LDB >= 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, U(k,k) is exactly zero. The factorization* has been completed, but the factor U is exactly* singular, so the solution could not be computed.** =====================================================================** .. External Subroutines .. EXTERNAL DGETRF, DGETRS, XERBLA* ..* .. Intrinsic Functions .. INTRINSIC MAX* ..* .. Executable Statements ..** Test the input parameters.* INFO = 0 IF( N.LT.0 ) THEN INFO = -1 ELSE IF( NRHS.LT.0 ) THEN INFO = -2 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN INFO = -4 ELSE IF( LDB.LT.MAX( 1, N ) ) THEN INFO = -7 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'DGESV ', -INFO ) RETURN END IF** Compute the LU factorization of A.* CALL DGETRF( N, N, A, LDA, IPIV, INFO ) IF( INFO.EQ.0 ) THEN** Solve the system A*X = B, overwriting B with X.* CALL DGETRS( 'No transpose', N, NRHS, A, LDA, IPIV, B, LDB, $ INFO ) END IF RETURN** End of DGESV* END SUBROUTINE DGETF2( M, N, A, LDA, IPIV, INFO )** -- LAPACK routine (version 1.0) --* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,* Courant Institute, Argonne National Lab, and Rice University* February 29, 1992** .. Scalar Arguments .. INTEGER INFO, LDA, M, N* ..* .. Array Arguments .. INTEGER IPIV( * ) DOUBLE PRECISION A( LDA, * )* ..** Purpose* =======** DGETF2 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) DOUBLE PRECISION 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 .. DOUBLE PRECISION ONE, ZERO PARAMETER ( ONE = 1D+0, ZERO = 0D+0 )* ..* .. Local Scalars .. INTEGER J, JP* ..* .. External Functions .. INTEGER IDAMAX EXTERNAL IDAMAX* ..* .. External Subroutines .. EXTERNAL DGER, DSCAL, DSWAP, XERBLA* ..* .. 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( 'DGETF2', -INFO ) RETURN END IF** Quick return if possible* IF( M.EQ.0 .OR. N.EQ.0 ) $ RETURN* DO 10 J = 1, MIN( M, N )** Find pivot and test for singularity.* JP = J - 1 + IDAMAX( 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 DSWAP( N, A( J, 1 ), LDA, A( JP, 1 ), LDA )** Compute elements J+1:M of J-th column.* IF( J.LT.M ) $ CALL DSCAL( M-J, ONE / A( J, J ), A( J+1, J ), 1 )* ELSE IF( INFO.EQ.0 ) THEN* INFO = J END IF* IF( J+1.LE.N ) THEN** Update trailing submatrix.* CALL DGER( 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 DGETF2* END SUBROUTINE DGETRF( M, N, A, LDA, IPIV, INFO )** -- LAPACK routine (version 3.0) --* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,* Courant Institute, Argonne National Lab, and Rice University* March 31, 1993** .. Scalar Arguments .. INTEGER INFO, LDA, M, N* ..* .. Array Arguments .. INTEGER IPIV( * ) DOUBLE PRECISION A( LDA, * )* ..** Purpose* =======** DGETRF 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 3 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) DOUBLE PRECISION 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 = -i, the i-th argument had an illegal value* > 0: if INFO = i, U(i,i) 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 .. DOUBLE PRECISION ONE PARAMETER ( ONE = 1D+0 )* ..* .. Local Scalars .. INTEGER I, IINFO, J, JB, NB* ..* .. External Subroutines .. EXTERNAL DGEMM, DGETF2, DLASWP, DTRSM, XERBLA* ..* .. External Functions .. INTEGER ILAENV EXTERNAL ILAENV* ..* .. 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( 'DGETRF', -INFO ) RETURN END IF** Quick return if possible* IF( M.EQ.0 .OR. N.EQ.0 ) $ RETURN** Determine the block size for this environment.* NB = ILAENV( 1, 'DGETRF', ' ', M, N, -1, -1 ) IF( NB.LE.1 .OR. NB.GE.MIN( M, N ) ) THEN** Use unblocked code.* CALL DGETF2( M, N, A, LDA, IPIV, INFO ) ELSE** Use blocked code.* DO 20 J = 1, MIN( M, N ), NB JB = MIN( MIN( M, N )-J+1, NB )** Factor diagonal and subdiagonal blocks and test for exact* singularity.* CALL DGETF2( M-J+1, JB, A( J, J ), LDA, IPIV( J ), IINFO )** Adjust INFO and the pivot indices.* IF( INFO.EQ.0 .AND. IINFO.GT.0 ) $ INFO = IINFO + J - 1 DO 10 I = J, MIN( M, J+JB-1 ) IPIV( I ) = J - 1 + IPIV( I ) 10 CONTINUE** Apply interchanges to columns 1:J-1.* CALL DLASWP( J-1, A, LDA, J, J+JB-1, IPIV, 1 )* IF( J+JB.LE.N ) THEN** Apply interchanges to columns J+JB:N.* CALL DLASWP( N-J-JB+1, A( 1, J+JB ), LDA, J, J+JB-1, $ IPIV, 1 )** Compute block row of U.* CALL DTRSM( 'Left', 'Lower', 'No transpose', 'Unit', JB, $ N-J-JB+1, ONE, A( J, J ), LDA, A( J, J+JB ), $ LDA ) IF( J+JB.LE.M ) THEN** Update trailing submatrix.* CALL DGEMM( 'No transpose', 'No transpose', M-J-JB+1, $ N-J-JB+1, JB, -ONE, A( J+JB, J ), LDA, $ A( J, J+JB ), LDA, ONE, A( J+JB, J+JB ), $ LDA )
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