sget54()

subroutine sget54	(	integer	n,
		real, dimension( lda, * )	a,
		integer	lda,
		real, dimension( ldb, * )	b,
		integer	ldb,
		real, dimension( lds, * )	s,
		integer	lds,
		real, dimension( ldt, * )	t,
		integer	ldt,
		real, dimension( ldu, * )	u,
		integer	ldu,
		real, dimension( ldv, * )	v,
		integer	ldv,
		real, dimension( * )	work,
		real	result
	)

SGET54

Purpose:

 SGET54 checks a generalized decomposition of the form

          A = U*S*V'  and B = U*T* V'

 where ' means transpose and U and V are orthogonal.

 Specifically,

  RESULT = ||( A - U*S*V', B - U*T*V' )|| / (||( A, B )||*n*ulp )

Parameters

[in]	N	N is INTEGER The size of the matrix. If it is zero, SGET54 does nothing. It must be at least zero.
[in]	A	A is REAL array, dimension (LDA, N) The original (unfactored) matrix A.
[in]	LDA	LDA is INTEGER The leading dimension of A. It must be at least 1 and at least N.
[in]	B	B is REAL array, dimension (LDB, N) The original (unfactored) matrix B.
[in]	LDB	LDB is INTEGER The leading dimension of B. It must be at least 1 and at least N.
[in]	S	S is REAL array, dimension (LDS, N) The factored matrix S.
[in]	LDS	LDS is INTEGER The leading dimension of S. It must be at least 1 and at least N.
[in]	T	T is REAL array, dimension (LDT, N) The factored matrix T.
[in]	LDT	LDT is INTEGER The leading dimension of T. It must be at least 1 and at least N.
[in]	U	U is REAL array, dimension (LDU, N) The orthogonal matrix on the left-hand side in the decomposition.
[in]	LDU	LDU is INTEGER The leading dimension of U. LDU must be at least N and at least 1.
[in]	V	V is REAL array, dimension (LDV, N) The orthogonal matrix on the left-hand side in the decomposition.
[in]	LDV	LDV is INTEGER The leading dimension of V. LDV must be at least N and at least 1.
[out]	WORK	WORK is REAL array, dimension (3*N**2)
[out]	RESULT	RESULT is REAL The value RESULT, It is currently limited to 1/ulp, to avoid overflow. Errors are flagged by RESULT=10/ulp.

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 154 of file sget54.f.

*
*  -- LAPACK test routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      INTEGER            LDA, LDB, LDS, LDT, LDU, LDV, N
      REAL               RESULT
*     ..
*     .. Array Arguments ..
      REAL               A( LDA, * ), B( LDB, * ), S( LDS, * ),
     $                   T( LDT, * ), U( LDU, * ), V( LDV, * ),
     $                   WORK( * )
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      REAL               ZERO, ONE
      parameter( zero = 0.0e+0, one = 1.0e+0 )
*     ..
*     .. Local Scalars ..
      REAL               ABNORM, ULP, UNFL, WNORM
*     ..
*     .. Local Arrays ..
      REAL               DUM( 1 )
*     ..
*     .. External Functions ..
      REAL               SLAMCH, SLANGE
      EXTERNAL           slamch, slange
*     ..
*     .. External Subroutines ..
      EXTERNAL           sgemm, slacpy
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          max, min, real
*     ..
*     .. Executable Statements ..
*
      result = zero
      IF( n.LE.0 )
     $   RETURN
*
*     Constants
*
      unfl = slamch( 'Safe minimum' )
      ulp = slamch( 'Epsilon' )*slamch( 'Base' )
*
*     compute the norm of (A,B)
*
      CALL slacpy( 'Full', n, n, a, lda, work, n )
      CALL slacpy( 'Full', n, n, b, ldb, work( n*n+1 ), n )
      abnorm = max( slange( '1', n, 2*n, work, n, dum ), unfl )
*
*     Compute W1 = A - U*S*V', and put in the array WORK(1:N*N)
*
      CALL slacpy( ' ', n, n, a, lda, work, n )
      CALL sgemm( 'N', 'N', n, n, n, one, u, ldu, s, lds, zero,
     $            work( n*n+1 ), n )
*
      CALL sgemm( 'N', 'C', n, n, n, -one, work( n*n+1 ), n, v, ldv,
     $            one, work, n )
*
*     Compute W2 = B - U*T*V', and put in the workarray W(N*N+1:2*N*N)
*
      CALL slacpy( ' ', n, n, b, ldb, work( n*n+1 ), n )
      CALL sgemm( 'N', 'N', n, n, n, one, u, ldu, t, ldt, zero,
     $            work( 2*n*n+1 ), n )
*
      CALL sgemm( 'N', 'C', n, n, n, -one, work( 2*n*n+1 ), n, v, ldv,
     $            one, work( n*n+1 ), n )
*
*     Compute norm(W)/ ( ulp*norm((A,B)) )
*
      wnorm = slange( '1', n, 2*n, work, n, dum )
*
      IF( abnorm.GT.wnorm ) THEN
         result = ( wnorm / abnorm ) / ( 2*n*ulp )
      ELSE
         IF( abnorm.LT.one ) THEN
            result = ( min( wnorm, 2*n*abnorm ) / abnorm ) / ( 2*n*ulp )
         ELSE
            result = min( wnorm / abnorm, real( 2*n ) ) / ( 2*n*ulp )
         END IF
      END IF
*
      RETURN
*
*     End of SGET54
*

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