How to find error between two figures?

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Answer 1

[Walter Roberson]

You can change the lines

w=a*r.^2/(2*nu);
w0=a*r0^2/(2*nu);
theta=-Gamm_inf/(8*pi*nu)*(1/w0*(1-exp(-w0))-(1./w.*(1-exp(-w)))-expint(w)-expint(w0));
[x1, y1]=pol2cart(theta,r);

slightly to somethng like

w = @(r) a*r.^2/(2*nu);
w0 = a*r0^2/(2*nu);
theta = @(r) -Gamm_inf/(8*pi*nu)*(1/w0*(1-exp(-w0))-(1./w(r).*(1-exp(-w(r))))-expint(w(r))-expint(w0));
[x1, y1]=pol2cart(theta(r),r);

Then after you have done

R = Y(:,1);
THETA = Y(:,2);

you can also do

THETA_exact = theta(R);
[x1_diff, y1_diff] = pol2cart(THETA_exact - THETA, R);
figure()
plot(x1_diff, y1_diff)