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dlae2 (3)
  • >> dlae2 (3) ( Solaris man: Библиотечные вызовы )
  • 
    NAME
         dlae2 - compute the eigenvalues of a 2-by-2 symmetric matrix
         [ A B ]  [ B C ]
    
    SYNOPSIS
         SUBROUTINE DLAE2( A, B, C, RT1, RT2 )
    
         DOUBLE PRECISION A, B, C, RT1, RT2
    
    
    
         #include <sunperf.h>
    
         void dlae2(double a, double b, double c, double *rt1, double
                   *rt2) ;
    
    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 abso-
         lute value.
    
    
    ARGUMENTS
         A         (input) DOUBLE PRECISION
                   The (1,1) element of the 2-by-2 matrix.
    
         B         (input) DOUBLE PRECISION
                   The (1,2) and (2,1) elements of the 2-by-2 matrix.
    
         C         (input) DOUBLE PRECISION
                   The (2,2) element of the 2-by-2 matrix.
    
         RT1       (output) DOUBLE PRECISION
                   The eigenvalue of larger absolute value.
    
         RT2       (output) DOUBLE PRECISION
                   The eigenvalue of smaller absolute value.
    
    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.
    
    
    
    


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