Subroutine */
| 12874 | } /* dlaeda_ */ |
| 12875 | |
| 12876 | /* Subroutine */ int dlaev2_(doublereal *a, doublereal *b, doublereal *c__, |
| 12877 | doublereal *rt1, doublereal *rt2, doublereal *cs1, doublereal *sn1) |
| 12878 | { |
| 12879 | /* System generated locals */ |
| 12880 | doublereal d__1; |
| 12881 | |
| 12882 | /* Local variables */ |
| 12883 | static doublereal ab, df, cs, ct, tb, sm, tn, rt, adf, acs; |
| 12884 | static integer sgn1, sgn2; |
| 12885 | static doublereal acmn, acmx; |
| 12886 | |
| 12887 | |
| 12888 | /* |
| 12889 | -- LAPACK auxiliary routine (version 3.2) -- |
| 12890 | -- LAPACK is a software package provided by Univ. of Tennessee, -- |
| 12891 | -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- |
| 12892 | November 2006 |
| 12893 | |
| 12894 | |
| 12895 | Purpose |
| 12896 | ======= |
| 12897 | |
| 12898 | DLAEV2 computes the eigendecomposition of a 2-by-2 symmetric matrix |
| 12899 | [ A B ] |
| 12900 | [ B C ]. |
| 12901 | On return, RT1 is the eigenvalue of larger absolute value, RT2 is the |
| 12902 | eigenvalue of smaller absolute value, and (CS1,SN1) is the unit right |
| 12903 | eigenvector for RT1, giving the decomposition |
| 12904 | |
| 12905 | [ CS1 SN1 ] [ A B ] [ CS1 -SN1 ] = [ RT1 0 ] |
| 12906 | [-SN1 CS1 ] [ B C ] [ SN1 CS1 ] [ 0 RT2 ]. |
| 12907 | |
| 12908 | Arguments |
| 12909 | ========= |
| 12910 | |
| 12911 | A (input) DOUBLE PRECISION |
| 12912 | The (1,1) element of the 2-by-2 matrix. |
| 12913 | |
| 12914 | B (input) DOUBLE PRECISION |
| 12915 | The (1,2) element and the conjugate of the (2,1) element of |
| 12916 | the 2-by-2 matrix. |
| 12917 | |
| 12918 | C (input) DOUBLE PRECISION |
| 12919 | The (2,2) element of the 2-by-2 matrix. |
| 12920 | |
| 12921 | RT1 (output) DOUBLE PRECISION |
| 12922 | The eigenvalue of larger absolute value. |
| 12923 | |
| 12924 | RT2 (output) DOUBLE PRECISION |
| 12925 | The eigenvalue of smaller absolute value. |
| 12926 | |
| 12927 | CS1 (output) DOUBLE PRECISION |
| 12928 | SN1 (output) DOUBLE PRECISION |
| 12929 | The vector (CS1, SN1) is a unit right eigenvector for RT1. |
| 12930 | |
| 12931 | Further Details |
| 12932 | =============== |
| 12933 |