subroutine rsb(nm,n,mb,a,w,matz,z,fv1,fv2,ierr)
c
integer n,mb,nm,ierr,matz
double precision a(nm,mb),w(n),z(nm,n),fv1(n),fv2(n)
logical tf
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 band 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 mb is the half band width of the matrix, defined as the
c number of adjacent diagonals, including the principal
c diagonal, required to specify the non-zero portion of the
c lower triangle of the matrix.
c
c a contains the lower triangle of the real symmetric
c band matrix. its lowest subdiagonal is stored in the
c last n+1-mb positions of the first column, its next
c subdiagonal in the last n+2-mb positions of the
c second column, further subdiagonals similarly, and
c finally its principal diagonal in the n positions
c of the last column. contents of storages not part
c of the matrix are arbitrary.
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 5
ierr = 10 * n
go to 50
5 if (mb .gt. 0) go to 10
ierr = 12 * n
go to 50
10 if (mb .le. n) go to 15
ierr = 12 * n
go to 50
c
15 if (matz .ne. 0) go to 20
c .......... find eigenvalues only ..........
tf = .false.
call bandr(nm,n,mb,a,w,fv1,fv2,tf,z)
call tqlrat(n,w,fv2,ierr)
go to 50
c .......... find both eigenvalues and eigenvectors ..........
20 tf = .true.
call bandr(nm,n,mb,a,w,fv1,fv1,tf,z)
call tql2(nm,n,w,fv1,z,ierr)
50 return
end