Developer Reference for Intel® oneAPI Math Kernel Library for Fortran
?lae2
Computes the eigenvalues of a 2-by-2 symmetric matrix.
Syntax
call slae2 ( a , b , c , rt1 , rt2 )
call dlae2 ( a , b , c , rt1 , rt2 )
Include Files
mkl.fi
Description
slae2 dlae2
The routines sla2 / dlae2 compute the eigenvalues of a 2-by-2 symmetric matrix
On return, rt1 is the eigenvalue of larger absolute value, and rt1 is the eigenvalue of smaller absolute value.
Input Parameters
- a , b , c
-
REAL for slae2 DOUBLE PRECISION for dlae2 The elements a , b , and c of the 2-by-2 matrix above.
Output Parameters
- rt1 , rt2
-
REAL for slae2 DOUBLE PRECISION for dlae2 The computed eigenvalues of larger and smaller absolute value, respectively.
Application Notes
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 .