rs.f
59 lines
| 1.9 KiB
| text/x-fortran
|
FortranFixedLexer
| r1601 | subroutine rs(nm,n,a,w,matz,z,fv1,fv2,ierr) | |||
| c | ||||
| integer n,nm,ierr,matz | ||||
| double precision a(nm,n),w(n),z(nm,n),fv1(n),fv2(n) | ||||
| c | ||||
| c this subroutine calls the recommended sequence of | ||||
| c subroutines from the eigensystem subroutine package (eispack) | ||||
| c to find the eigenvalues and eigenvectors (if desired) | ||||
| c of a real symmetric matrix. | ||||
| c | ||||
| c on input | ||||
| c | ||||
| c nm must be set to the row dimension of the two-dimensional | ||||
| c array parameters as declared in the calling program | ||||
| c dimension statement. | ||||
| c | ||||
| c n is the order of the matrix a. | ||||
| c | ||||
| c a contains the real symmetric matrix. | ||||
| c | ||||
| c matz is an integer variable set equal to zero if | ||||
| c only eigenvalues are desired. otherwise it is set to | ||||
| c any non-zero integer for both eigenvalues and eigenvectors. | ||||
| c | ||||
| c on output | ||||
| c | ||||
| c w contains the eigenvalues in ascending order. | ||||
| c | ||||
| c z contains the eigenvectors if matz is not zero. | ||||
| c | ||||
| c ierr is an integer output variable set equal to an error | ||||
| c completion code described in the documentation for tqlrat | ||||
| c and tql2. the normal completion code is zero. | ||||
| c | ||||
| c fv1 and fv2 are temporary storage arrays. | ||||
| c | ||||
| c questions and comments should be directed to burton s. garbow, | ||||
| c mathematics and computer science div, argonne national laboratory | ||||
| c | ||||
| c this version dated august 1983. | ||||
| c | ||||
| c ------------------------------------------------------------------ | ||||
| c | ||||
| if (n .le. nm) go to 10 | ||||
| ierr = 10 * n | ||||
| go to 50 | ||||
| c | ||||
| 10 if (matz .ne. 0) go to 20 | ||||
| c .......... find eigenvalues only .......... | ||||
| call tred1(nm,n,a,w,fv1,fv2) | ||||
| * tqlrat encounters catastrophic underflow on the Vax | ||||
| * call tqlrat(n,w,fv2,ierr) | ||||
| call tql1(n,w,fv1,ierr) | ||||
| go to 50 | ||||
| c .......... find both eigenvalues and eigenvectors .......... | ||||
| 20 call tred2(nm,n,a,w,fv1,z) | ||||
| call tql2(nm,n,w,fv1,z,ierr) | ||||
| 50 return | ||||
| end | ||||
