function [Ca,Cb,La,Lb] = ploteig(A,range)
% Plots the eigenvectors for a 2-D coefficient matrix A

% test for size
[m,n] = size(A);
if m ~= 2 | n ~= 2
   'Matrix is not 2-D - quitting.'
   return
end

% eigenanalysis and test for real result
[c,l] = eig(A);
Ca = c(:,1);
Cb = c(:,2);
La = l(1,1);
Lb = l(2,2);
if ~isreal(c)
   'Eigenvectors/values are imaginary - quitting.'
   return
end

% eigenvector A
x = -range:range;
slope = Ca(2)/Ca(1);
y = slope*x;
clf;
hold on;
grid;
plot(x,y,'r-');

%eigenvector B
slope = Cb(2)/Cb(1);
y = slope*x;
plot(x,y,'b-');