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slae2.f(3) LAPACK slae2.f(3)

NAME

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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