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authorjofret2009-04-28 07:17:00 +0000
committerjofret2009-04-28 07:17:00 +0000
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- SUBROUTINE DLATDF( IJOB, N, Z, LDZ, RHS, RDSUM, RDSCAL, IPIV,
- $ JPIV )
-*
-* -- LAPACK auxiliary routine (version 3.1) --
-* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
-* November 2006
-*
-* .. Scalar Arguments ..
- INTEGER IJOB, LDZ, N
- DOUBLE PRECISION RDSCAL, RDSUM
-* ..
-* .. Array Arguments ..
- INTEGER IPIV( * ), JPIV( * )
- DOUBLE PRECISION RHS( * ), Z( LDZ, * )
-* ..
-*
-* Purpose
-* =======
-*
-* DLATDF uses the LU factorization of the n-by-n matrix Z computed by
-* DGETC2 and computes a contribution to the reciprocal Dif-estimate
-* by solving Z * x = b for x, and choosing the r.h.s. b such that
-* the norm of x is as large as possible. On entry RHS = b holds the
-* contribution from earlier solved sub-systems, and on return RHS = x.
-*
-* The factorization of Z returned by DGETC2 has the form Z = P*L*U*Q,
-* where P and Q are permutation matrices. L is lower triangular with
-* unit diagonal elements and U is upper triangular.
-*
-* Arguments
-* =========
-*
-* IJOB (input) INTEGER
-* IJOB = 2: First compute an approximative null-vector e
-* of Z using DGECON, e is normalized and solve for
-* Zx = +-e - f with the sign giving the greater value
-* of 2-norm(x). About 5 times as expensive as Default.
-* IJOB .ne. 2: Local look ahead strategy where all entries of
-* the r.h.s. b is choosen as either +1 or -1 (Default).
-*
-* N (input) INTEGER
-* The number of columns of the matrix Z.
-*
-* Z (input) DOUBLE PRECISION array, dimension (LDZ, N)
-* On entry, the LU part of the factorization of the n-by-n
-* matrix Z computed by DGETC2: Z = P * L * U * Q
-*
-* LDZ (input) INTEGER
-* The leading dimension of the array Z. LDA >= max(1, N).
-*
-* RHS (input/output) DOUBLE PRECISION array, dimension N.
-* On entry, RHS contains contributions from other subsystems.
-* On exit, RHS contains the solution of the subsystem with
-* entries acoording to the value of IJOB (see above).
-*
-* RDSUM (input/output) DOUBLE PRECISION
-* On entry, the sum of squares of computed contributions to
-* the Dif-estimate under computation by DTGSYL, where the
-* scaling factor RDSCAL (see below) has been factored out.
-* On exit, the corresponding sum of squares updated with the
-* contributions from the current sub-system.
-* If TRANS = 'T' RDSUM is not touched.
-* NOTE: RDSUM only makes sense when DTGSY2 is called by STGSYL.
-*
-* RDSCAL (input/output) DOUBLE PRECISION
-* On entry, scaling factor used to prevent overflow in RDSUM.
-* On exit, RDSCAL is updated w.r.t. the current contributions
-* in RDSUM.
-* If TRANS = 'T', RDSCAL is not touched.
-* NOTE: RDSCAL only makes sense when DTGSY2 is called by
-* DTGSYL.
-*
-* IPIV (input) INTEGER array, dimension (N).
-* The pivot indices; for 1 <= i <= N, row i of the
-* matrix has been interchanged with row IPIV(i).
-*
-* JPIV (input) INTEGER array, dimension (N).
-* The pivot indices; for 1 <= j <= N, column j of the
-* matrix has been interchanged with column JPIV(j).
-*
-* Further Details
-* ===============
-*
-* Based on contributions by
-* Bo Kagstrom and Peter Poromaa, Department of Computing Science,
-* Umea University, S-901 87 Umea, Sweden.
-*
-* This routine is a further developed implementation of algorithm
-* BSOLVE in [1] using complete pivoting in the LU factorization.
-*
-* [1] Bo Kagstrom and Lars Westin,
-* Generalized Schur Methods with Condition Estimators for
-* Solving the Generalized Sylvester Equation, IEEE Transactions
-* on Automatic Control, Vol. 34, No. 7, July 1989, pp 745-751.
-*
-* [2] Peter Poromaa,
-* On Efficient and Robust Estimators for the Separation
-* between two Regular Matrix Pairs with Applications in
-* Condition Estimation. Report IMINF-95.05, Departement of
-* Computing Science, Umea University, S-901 87 Umea, Sweden, 1995.
-*
-* =====================================================================
-*
-* .. Parameters ..
- INTEGER MAXDIM
- PARAMETER ( MAXDIM = 8 )
- DOUBLE PRECISION ZERO, ONE
- PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0 )
-* ..
-* .. Local Scalars ..
- INTEGER I, INFO, J, K
- DOUBLE PRECISION BM, BP, PMONE, SMINU, SPLUS, TEMP
-* ..
-* .. Local Arrays ..
- INTEGER IWORK( MAXDIM )
- DOUBLE PRECISION WORK( 4*MAXDIM ), XM( MAXDIM ), XP( MAXDIM )
-* ..
-* .. External Subroutines ..
- EXTERNAL DAXPY, DCOPY, DGECON, DGESC2, DLASSQ, DLASWP,
- $ DSCAL
-* ..
-* .. External Functions ..
- DOUBLE PRECISION DASUM, DDOT
- EXTERNAL DASUM, DDOT
-* ..
-* .. Intrinsic Functions ..
- INTRINSIC ABS, SQRT
-* ..
-* .. Executable Statements ..
-*
- IF( IJOB.NE.2 ) THEN
-*
-* Apply permutations IPIV to RHS
-*
- CALL DLASWP( 1, RHS, LDZ, 1, N-1, IPIV, 1 )
-*
-* Solve for L-part choosing RHS either to +1 or -1.
-*
- PMONE = -ONE
-*
- DO 10 J = 1, N - 1
- BP = RHS( J ) + ONE
- BM = RHS( J ) - ONE
- SPLUS = ONE
-*
-* Look-ahead for L-part RHS(1:N-1) = + or -1, SPLUS and
-* SMIN computed more efficiently than in BSOLVE [1].
-*
- SPLUS = SPLUS + DDOT( N-J, Z( J+1, J ), 1, Z( J+1, J ), 1 )
- SMINU = DDOT( N-J, Z( J+1, J ), 1, RHS( J+1 ), 1 )
- SPLUS = SPLUS*RHS( J )
- IF( SPLUS.GT.SMINU ) THEN
- RHS( J ) = BP
- ELSE IF( SMINU.GT.SPLUS ) THEN
- RHS( J ) = BM
- ELSE
-*
-* In this case the updating sums are equal and we can
-* choose RHS(J) +1 or -1. The first time this happens
-* we choose -1, thereafter +1. This is a simple way to
-* get good estimates of matrices like Byers well-known
-* example (see [1]). (Not done in BSOLVE.)
-*
- RHS( J ) = RHS( J ) + PMONE
- PMONE = ONE
- END IF
-*
-* Compute the remaining r.h.s.
-*
- TEMP = -RHS( J )
- CALL DAXPY( N-J, TEMP, Z( J+1, J ), 1, RHS( J+1 ), 1 )
-*
- 10 CONTINUE
-*
-* Solve for U-part, look-ahead for RHS(N) = +-1. This is not done
-* in BSOLVE and will hopefully give us a better estimate because
-* any ill-conditioning of the original matrix is transfered to U
-* and not to L. U(N, N) is an approximation to sigma_min(LU).
-*
- CALL DCOPY( N-1, RHS, 1, XP, 1 )
- XP( N ) = RHS( N ) + ONE
- RHS( N ) = RHS( N ) - ONE
- SPLUS = ZERO
- SMINU = ZERO
- DO 30 I = N, 1, -1
- TEMP = ONE / Z( I, I )
- XP( I ) = XP( I )*TEMP
- RHS( I ) = RHS( I )*TEMP
- DO 20 K = I + 1, N
- XP( I ) = XP( I ) - XP( K )*( Z( I, K )*TEMP )
- RHS( I ) = RHS( I ) - RHS( K )*( Z( I, K )*TEMP )
- 20 CONTINUE
- SPLUS = SPLUS + ABS( XP( I ) )
- SMINU = SMINU + ABS( RHS( I ) )
- 30 CONTINUE
- IF( SPLUS.GT.SMINU )
- $ CALL DCOPY( N, XP, 1, RHS, 1 )
-*
-* Apply the permutations JPIV to the computed solution (RHS)
-*
- CALL DLASWP( 1, RHS, LDZ, 1, N-1, JPIV, -1 )
-*
-* Compute the sum of squares
-*
- CALL DLASSQ( N, RHS, 1, RDSCAL, RDSUM )
-*
- ELSE
-*
-* IJOB = 2, Compute approximate nullvector XM of Z
-*
- CALL DGECON( 'I', N, Z, LDZ, ONE, TEMP, WORK, IWORK, INFO )
- CALL DCOPY( N, WORK( N+1 ), 1, XM, 1 )
-*
-* Compute RHS
-*
- CALL DLASWP( 1, XM, LDZ, 1, N-1, IPIV, -1 )
- TEMP = ONE / SQRT( DDOT( N, XM, 1, XM, 1 ) )
- CALL DSCAL( N, TEMP, XM, 1 )
- CALL DCOPY( N, XM, 1, XP, 1 )
- CALL DAXPY( N, ONE, RHS, 1, XP, 1 )
- CALL DAXPY( N, -ONE, XM, 1, RHS, 1 )
- CALL DGESC2( N, Z, LDZ, RHS, IPIV, JPIV, TEMP )
- CALL DGESC2( N, Z, LDZ, XP, IPIV, JPIV, TEMP )
- IF( DASUM( N, XP, 1 ).GT.DASUM( N, RHS, 1 ) )
- $ CALL DCOPY( N, XP, 1, RHS, 1 )
-*
-* Compute the sum of squares
-*
- CALL DLASSQ( N, RHS, 1, RDSCAL, RDSUM )
-*
- END IF
-*
- RETURN
-*
-* End of DLATDF
-*
- END