SRC/dlae2.f(3)

NAME
SRC/dlae2.f

SYNOPSIS

  Functions/Subroutines
subroutine dlae2 (a, b, c, rt1, rt2)
DLAE2 computes the eigenvalues of a 2-by-2 symmetric matrix.

Function/Subroutine Documentation

  subroutine dlae2 (double precision a, double precision b, double precision c, double precision rt1, double precision rt2)

DLAE2 computes the eigenvalues of a 2-by-2 symmetric matrix.

Purpose:

     DLAE2  computes the eigenvalues of a 2-by-2 symmetric matrix
        [  A   B  ]
        [  B   C  ].
     On return, RT1 is the eigenvalue of larger absolute value, and RT2
     is the eigenvalue of smaller absolute value.

Parameters
    A

              A is DOUBLE PRECISION
              The (1,1) element of the 2-by-2 matrix.

    B

              B is DOUBLE PRECISION
              The (1,2) and (2,1) elements of the 2-by-2 matrix.

    C

              C is DOUBLE PRECISION
              The (2,2) element of the 2-by-2 matrix.

    RT1

              RT1 is DOUBLE PRECISION
              The eigenvalue of larger absolute value.

    RT2

              RT2 is DOUBLE PRECISION
              The eigenvalue of smaller absolute value.

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

      RT1 is accurate to a few ulps barring over/underflow.
      RT2 may be inaccurate if there is massive cancellation in the
      determinant A*C-B*B; higher precision or correctly rounded or
      correctly truncated arithmetic would be needed to compute RT2
      accurately in all cases.
      Overflow is possible only if RT1 is within a factor of 5 of overflow.
      Underflow is harmless if the input data is 0 or exceeds
         underflow_threshold / macheps.

Definition at line 101 of file dlae2.f.

Author

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