Contour plot of a function

Please someone should with a contour plot of a p for various values of xi and H. For instance, H=0..3, and xi=2.0..0.0, where H is the x-axis, xi is the y-axis and p is the height of the contour. I need r to compute p, that is why write the expression for r.

for i = 1:m

q = x +i*y;

r(i)=q-(1-alpha)*tan(q)+(alpha3*xi*alpha/eta1)./(4*k1*q.^2/d^2-alpha3*xi/eta1).*tan(q)...

+ ((chi_a*H.^2*alpha)./(4*k1*q.^2/d^2-alpha3*xi/eta1 - chi_a*H.^2)).*tan(q);

end

for i=1:m

p(i) = gamma1*alpha/(4*k1*(r(i).^2)/d^2-alpha3*xi/eta1);

end

Answer 1

[Torsten]

H = 0:0.01:3;
XI = 0:0.01:2;
for i=1:numel(H)
  h = H(i);
  for j=1:numel(XI)
    xi = XI(j);
    for k=1:m
      q = x +k*y;
      r = q-(1-alpha)*tan(q)+(alpha3*xi*alpha/eta1)./(4*k1*q.^2/d^2-alpha3*xi/eta1).*tan(q)...
          + ((chi_a*H.^2*alpha)./(4*k1*q.^2/d^2-alpha3*xi/eta1 - chi_a*H.^2)).*tan(q);
      p(i,j,k) = gamma1*alpha/(4*k1*(r^2)/d^2-alpha3*xi/eta1);
    end
  end
end

Now p is 3-dimensional instead of 2-dimensional as required for a contour plot. What now ?

[University Glasgow]

Thank you for your response. It seems you changed q=x+i*y. q is complex number here. How is x+i*y = x+k*y? Does matlab sees k as imaginary?

[Torsten]

You have a loop over i in your code to determine r(i) - thus the loop index is taken for i and not the complex unit.

If you want to use the complex unit, use

q = x +1i*y;

instead of

q = x +k*y;

in the above code.

In this case I wonder why you need a loop over i in your code - the index i appears nowhere in the expression for r(i).

[University Glasgow]

Thank you. I think I understand what is happening.

[Torsten]

So you have x1, x2, H and xi given over an interval of values and thus r (resp. p) depending on 4 parameters. If you want to plot a surface over H and xi, you must set x1 and x2 to a constant value and do the same for H and xi what you did for x1 and x2 in your code from above.

[Torsten]

@University Glasgow comment moved here:

Okay, thank you