slae2.f man page

slae2.f —

Synopsis

Functions/Subroutines

subroutine slae2 (A, B, C, RT1, RT2)
SLAE2 computes the eigenvalues of a 2-by-2 symmetric matrix.

Function/Subroutine Documentation

subroutine slae2 (realA, realB, realC, realRT1, realRT2)

SLAE2 computes the eigenvalues of a 2-by-2 symmetric matrix.

Purpose:

SLAE2  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 REAL
The (1,1) element of the 2-by-2 matrix.

B

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

C

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

RT1

RT1 is REAL
The eigenvalue of larger absolute value.

RT2

RT2 is REAL
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 slae2.f.

Author

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Referenced By

slae2(3) is an alias of slae2.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK