dlae2.f (3) Linux Manual 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
B
The (1,1) element of the 2-by-2 matrix.B is DOUBLE PRECISION
C
The (1,2) and (2,1) elements of the 2-by-2 matrix.C is DOUBLE PRECISION
RT1
The (2,2) element of the 2-by-2 matrix.RT1 is DOUBLE PRECISION
RT2
The eigenvalue of larger absolute value.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.