MATLAB Function Reference Volume 1: A - E - Bad Request

eigs
2-476
eigs(Afun,n,k,sigma,opts,p1,p2,...) and
eigs(Afun,n,B,k,sigma,opts,p1,p2,...) provide for additional arguments
which are passed to Afun(x,p1,p2,...).
Remarks d = eigs(A,k) is not a substitute for
d = eig(full(A))
d = sort(d)
d = d(end-k+1:end)
but is most appropriate for large sparse matrices. If the problem fits into
memory, it may be quicker to use eig(full(A)).
Algorithm eigs provides the reverse communication required by the Fortran library
ARPACK, namely the routines DSAUPD, DSEUPD, DNAUPD, DNEUPD, ZNAUPD, and
ZNEUPD.
Examples Example 1: This example shows the use of function handles.
A = delsq(numgrid('C',15));
d1 = eigs(A,5,'sm');
Equivalently, if dnRk is the following one-line function:
function y = dnRk(x,R,k)
y = (delsq(numgrid(R,k))) * x;
then pass dnRk's additional arguments, 'C' and 15, to eigs.
n = size(A,1);
opts.issym = 1;
d2 = eigs(@dnRk,n,5,'sm',opts,'C',15);
Example 2: west0479 is a real 479-by-479 sparse matrix with both real and
pairs of complex conjugate eigenvalues. eig computes all 479 eigenvalues. eigs
easily picks out the largest magnitude eigenvalues.
This plot shows the 8 largest magnitude eigenvalues of west0479 as computed
by eig and eigs.
load west0479
d = eig(full(west0479))
dlm = eigs(west0479,8)