%
%  code3Ma.m -- 16 sept 02 -- djm
%
%  contour plotter

%  clear workspace & graphics

clear;  close all

%  set t & v grid matrices ("help meshgrid")

x = -5:0.05:5;  y = -5.025:0.05:5.025;
[xx,yy] = meshgrid(x,y);

%  calculate constant (matrix arithmetic, use , .* etc)

K = -1./yy - cos(xx);

%  plot tangent vectors ("help quiver") 

figure(1);  hold on
contour(x,y,K,[0 0],'k')
contour(x,y,K,[-2.0:0.5:-0.5],'r--')
contour(x,y,K,[0.5:0.5:2.0],'r')
axis([-5 5 -5 5])

%  label plot

title(['\bf ODE solutions (prob 2.2.3)'])
xlabel('x-axis')
ylabel('y-axis (K=0 in black, K<0 in red dash, K>0 in red solid)')