108 lines
3.2 KiB
Fortran
108 lines
3.2 KiB
Fortran
SUBROUTINE SGESVF( N, NRHS, A, LDA, IPIV, B, LDB, INFO )
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*
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* -- LAPACK driver 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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INTEGER INFO, LDA, LDB, N, NRHS
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* ..
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* .. Array Arguments ..
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INTEGER IPIV( * )
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REAL A( LDA, * ), B( LDB, * )
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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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* SGESV computes the solution to a real system of linear equations
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* A * X = B,
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* where A is an N-by-N matrix and X and B are N-by-NRHS matrices.
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*
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* The LU decomposition with partial pivoting and row interchanges is
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* used to factor A as
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* A = P * L * U,
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* where P is a permutation matrix, L is unit lower triangular, and U is
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* upper triangular. The factored form of A is then used to solve the
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* system of equations A * X = B.
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*
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* Arguments
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* =========
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*
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* N (input) INTEGER
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* The number of linear equations, i.e., the order of the
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* matrix A. N >= 0.
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*
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* NRHS (input) INTEGER
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* The number of right hand sides, i.e., the number of columns
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* of the matrix B. NRHS >= 0.
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*
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* A (input/output) REAL array, dimension (LDA,N)
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* On entry, the N-by-N coefficient matrix A.
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* On exit, the factors L and U from the factorization
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* A = P*L*U; the unit diagonal elements of L are not stored.
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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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* IPIV (output) INTEGER array, dimension (N)
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* The pivot indices that define the permutation matrix P;
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* row i of the matrix was interchanged with row IPIV(i).
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*
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* B (input/output) REAL array, dimension (LDB,NRHS)
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* On entry, the N-by-NRHS matrix of right hand side matrix B.
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* On exit, if INFO = 0, the N-by-NRHS solution matrix X.
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*
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* LDB (input) INTEGER
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* The leading dimension of the array B. LDB >= 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, U(i,i) is exactly zero. The factorization
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* has been completed, but the factor U is exactly
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* singular, so the solution could not be computed.
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*
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* =====================================================================
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*
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* .. External Subroutines ..
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EXTERNAL SGETRF, SGETRS, 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( N.LT.0 ) THEN
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INFO = -1
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ELSE IF( NRHS.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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ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
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INFO = -7
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END IF
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IF( INFO.NE.0 ) THEN
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CALL XERBLA( 'SGESV ', -INFO )
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RETURN
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END IF
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*
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* Compute the LU factorization of A.
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*
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CALL SGETRF( N, N, A, LDA, IPIV, INFO )
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IF( INFO.EQ.0 ) THEN
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*
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* Solve the system A*X = B, overwriting B with X.
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*
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CALL SGETRS( 'No transpose', N, NRHS, A, LDA, IPIV, B, LDB,
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$ INFO )
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END IF
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RETURN
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*
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* End of SGESV
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*
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END
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