% Plots the electric field vectors and equipotential contours
% to show the solution to a quasistatics problem.
%
% Colin Joye
% 6.641 (MIT)
% Problem Set: #6
% Problem: P6.2c
clear all;
clf(1);
[x,y] = meshgrid(-3:0.1:3,-6:0.2:6);
z = cos(y).*exp(-abs(x)); % Electric Field
[px,py] = gradient(z);    % Equipotential lines
[c,h]=contour(x,y,z); hold on
clabel(c);
colorbar;
x_=x(1:2:end,1:2:end);
y_=y(1:2:end,1:2:end);
px_=px(1:2:end,1:2:end);
py_=py(1:2:end,1:2:end);
plot([-3,3],[0,0],'k');
quiver(x_,y_,-px_,-py_); hold off; 
title(['Equipotential and Electric Field lines ' ...
   '(arbitrary scaling a=1), P6.2, Colin Joye']);
xlabel(['x']);
ylabel(['y']);
text(-2.8,1.7,['cos(ay)e^-^a^*^a^b^s^(^x^)=const']);
%----