Computes singular values of a 2-by-2 triangular matrix.
Syntax
call slas2( f, g, h, ssmin, ssmax )
call dlas2( f, g, h, ssmin, ssmax )
Include Files
- mkl.fi
Description
The routine ?las2 computes the singular values of the 2-by-2 matrix
On return, ssmin is the smaller singular value and SSMAX is the larger singular value.
Input Parameters
- f, g, h
REAL for slas2
DOUBLE PRECISION for dlas2
The (1,1), (1,2) and (2,2) elements of the 2-by-2 matrix, respectively.
Output Parameters
- ssmin, ssmax
REAL for slas2
DOUBLE PRECISION for dlas2
The smaller and the larger singular values, respectively.
Application Notes
Barring over/underflow, all output quantities are correct to within a few units in the last place (ulps), even in the absence of a guard digit in addition/subtraction. In ieee arithmetic, the code works correctly if one matrix element is infinite. Overflow will not occur unless the largest singular value itself overflows, or is within a few ulps of overflow. (On machines with partial overflow, like the Cray, overflow may occur if the largest singular value is within a factor of 2 of overflow.) Underflow is harmless if underflow is gradual. Otherwise, results may correspond to a matrix modified by perturbations of size near the underflow threshold.