dlae2.f (3) - Linux Manuals
NAME
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.
BB is DOUBLE PRECISION The (1,2) and (2,1) elements of the 2-by-2 matrix.
CC is DOUBLE PRECISION The (2,2) element of the 2-by-2 matrix.
RT1RT1 is DOUBLE PRECISION The eigenvalue of larger absolute value.
RT2RT2 is DOUBLE PRECISION The eigenvalue of smaller absolute value.
Author:
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Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
- September 2012
Further Details:
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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
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