TESTING/EIG/sget53.f(3)

NAME
TESTING/EIG/sget53.f

SYNOPSIS

  Functions/Subroutines
subroutine sget53 (a, lda, b, ldb, scale, wr, wi, result, info)
SGET53

Function/Subroutine Documentation

  subroutine sget53 (real, dimension( lda, * ) a, integer lda, real, dimension( ldb, * ) b, integer ldb, real scale, real wr, real wi, real result, integer info)

SGET53

Purpose:

     SGET53  checks the generalized eigenvalues computed by SLAG2.
     The basic test for an eigenvalue is:
                                  | det( s A - w B ) |
         RESULT =  ---------------------------------------------------
                   ulp max( s norm(A), |w| norm(B) )*norm( s A - w B )
     Two 'safety checks' are performed:
     (1)  ulp*max( s*norm(A), |w|*norm(B) )  must be at least
          safe_minimum.  This insures that the test performed is
          not essentially  det(0*A + 0*B)=0.
     (2)  s*norm(A) + |w|*norm(B) must be less than 1/safe_minimum.
          This insures that  s*A - w*B  will not overflow.
     If these tests are not passed, then  s  and  w  are scaled and
     tested anyway, if this is possible.

Parameters
    A

              A is REAL array, dimension (LDA, 2)
              The 2x2 matrix A.

    LDA

              LDA is INTEGER
              The leading dimension of A.  It must be at least 2.

    B

              B is REAL array, dimension (LDB, N)
              The 2x2 upper-triangular matrix B.

    LDB

              LDB is INTEGER
              The leading dimension of B.  It must be at least 2.

    SCALE

              SCALE is REAL
              The 'scale factor' s in the formula  s A - w B .  It is
              assumed to be non-negative.

    WR

              WR is REAL
              The real part of the eigenvalue  w  in the formula
              s A - w B .

    WI

              WI is REAL
              The imaginary part of the eigenvalue  w  in the formula
              s A - w B .

    RESULT

              RESULT is REAL
              If INFO is 2 or less, the value computed by the test
                 described above.
              If INFO=3, this will just be 1/ulp.

    INFO

              INFO is INTEGER
              =0:  The input data pass the 'safety checks'.
              =1:  s*norm(A) + |w|*norm(B) > 1/safe_minimum.
              =2:  ulp*max( s*norm(A), |w|*norm(B) ) < safe_minimum
              =3:  same as INFO=2, but  s  and  w  could not be scaled so
                   as to compute the test.

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 125 of file sget53.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.