dlae2.f man page

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 precisionA, double precisionB, double precisionC, double precisionRT1, double precisionRT2)

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.

Date:

September 2012

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 103 of file dlae2.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.

Referenced By

dlae2(3) is an alias of dlae2.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK