137 lines
3.8 KiB
FortranFixed
137 lines
3.8 KiB
FortranFixed
SUBROUTINE CGTT02( TRANS, N, NRHS, DL, D, DU, X, LDX, B, LDB,
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$ RWORK, RESID )
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*
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* -- LAPACK test 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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CHARACTER TRANS
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INTEGER LDB, LDX, N, NRHS
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REAL RESID
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* ..
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* .. Array Arguments ..
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REAL RWORK( * )
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COMPLEX B( LDB, * ), D( * ), DL( * ), DU( * ),
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$ X( LDX, * )
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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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* CGTT02 computes the residual for the solution to a tridiagonal
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* system of equations:
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* RESID = norm(B - op(A)*X) / (norm(A) * norm(X) * EPS),
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* where EPS is the machine epsilon.
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*
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* Arguments
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* =========
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*
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* TRANS (input) CHARACTER
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* Specifies the form of the residual.
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* = 'N': B - A * X (No transpose)
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* = 'T': B - A**T * X (Transpose)
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* = 'C': B - A**H * X (Conjugate transpose)
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*
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* N (input) INTEGTER
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* The order of the 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 matrices B and X. NRHS >= 0.
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*
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* DL (input) COMPLEX array, dimension (N-1)
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* The (n-1) sub-diagonal elements of A.
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*
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* D (input) COMPLEX array, dimension (N)
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* The diagonal elements of A.
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*
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* DU (input) COMPLEX array, dimension (N-1)
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* The (n-1) super-diagonal elements of A.
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*
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* X (input) COMPLEX array, dimension (LDX,NRHS)
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* The computed solution vectors X.
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*
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* LDX (input) INTEGER
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* The leading dimension of the array X. LDX >= max(1,N).
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*
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* B (input/output) COMPLEX array, dimension (LDB,NRHS)
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* On entry, the right hand side vectors for the system of
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* linear equations.
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* On exit, B is overwritten with the difference B - op(A)*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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* RWORK (workspace) REAL array, dimension (N)
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*
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* RESID (output) REAL
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* norm(B - op(A)*X) / (norm(A) * norm(X) * EPS)
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*
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* =====================================================================
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*
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* .. Parameters ..
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REAL ONE, ZERO
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PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 )
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* ..
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* .. Local Scalars ..
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INTEGER J
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REAL ANORM, BNORM, EPS, XNORM
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* ..
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* .. External Functions ..
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LOGICAL LSAME
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REAL CLANGT, SCASUM, SLAMCH
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EXTERNAL LSAME, CLANGT, SCASUM, SLAMCH
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* ..
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* .. External Subroutines ..
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EXTERNAL CLAGTM
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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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* Quick exit if N = 0 or NRHS = 0
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*
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RESID = ZERO
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IF( N.LE.0 .OR. NRHS.EQ.0 )
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$ RETURN
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*
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* Compute the maximum over the number of right hand sides of
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* norm(B - op(A)*X) / ( norm(A) * norm(X) * EPS ).
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*
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IF( LSAME( TRANS, 'N' ) ) THEN
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ANORM = CLANGT( '1', N, DL, D, DU )
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ELSE
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ANORM = CLANGT( 'I', N, DL, D, DU )
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END IF
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*
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* Exit with RESID = 1/EPS if ANORM = 0.
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*
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EPS = SLAMCH( 'Epsilon' )
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IF( ANORM.LE.ZERO ) THEN
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RESID = ONE / EPS
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RETURN
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END IF
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*
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* Compute B - op(A)*X.
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*
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CALL CLAGTM( TRANS, N, NRHS, -ONE, DL, D, DU, X, LDX, ONE, B,
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$ LDB )
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*
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DO 10 J = 1, NRHS
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BNORM = SCASUM( N, B( 1, J ), 1 )
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XNORM = SCASUM( N, X( 1, J ), 1 )
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IF( XNORM.LE.ZERO ) THEN
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RESID = ONE / EPS
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ELSE
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RESID = MAX( RESID, ( ( BNORM / ANORM ) / XNORM ) / EPS )
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END IF
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10 CONTINUE
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*
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RETURN
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*
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* End of CGTT02
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*
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END
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