updating knm test case

examples/knm.py

 import pykat
-from pykat.optics.knm import *
+from pykat.optics.knm import plot_knm_matrix, knmHG, makeCouplingMatrix
 from pykat.optics.maps import *
 import numpy as np
 
+q1 = pykat.BeamParam(w0=5e-2, z=0)
+q2 = pykat.BeamParam(w0=5e-2, z=0)
 
-C = makeCouplingMatrix(10)
+R  = max(q1.w, q2.w)
 
-q1 = pykat.BeamParam(w0=5e-2, z=0)
+N  = 500
+dx = R*6/N
+
+m = surfacemap("empty",
+               "phase both",
+               size=(N, N),
+               center=((N+1)/2, (N+1)/2),
+               step_size=(dx, dx))
+
+C = makeCouplingMatrix(2)
+
+K = knmHG(C, q1, q2, surface_map=m)
 
-K = knmHG(C, q1, q1, surface_map=m)
-plot_knm_matrix(C, abs(K))
\ No newline at end of file
+plot_knm_matrix(C, abs(K))