Trying to plot a radial contour

Question

Kelly 2013-2-16

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https://ww2.mathworks.cn/matlabcentral/answers/63742-trying-to-plot-a-radial-contour

I am trying to plot a 2x2 contour subplot, it is supposed to be circular, but I either get lines or no plot at all or an error saying my z needs to be a 2x2 array.

function F = ratio_rp_bf(R,theta,bD)
for r = 1:length(R)
  for b = 1:length(bD)
    F(b,r) = (16/3).*(1./bD(b)).*(1./R(r)).^3.*abs(sqrt((1./R(r)).^4-2.*(1./R(r)).^2.*cos(2.*theta(r))+1));
  end
end
bD = [0.1, 1.0, 10, 100];
R = (1:1.25:5);
c = R;
a = 1/2*bD;
b = abs(sqrt(c.^2 - a.^2));
theta = abs(atan(b./a));
[F] = ratio_rp_bf(R,theta,bD);
              for b = 1:length(bD)
               figure(1)
               subplot(2,2,b)
               x = R.*cos(theta);
               y = R.*sin(theta);
               z = F;
               [x,y,z] = meshgrid(x,y,z);
               [C,h] = contour(R,theta,bD,x,y,z);
               clabel(C,h);
               grid on
  end

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Answer 1

Thorsten 2013-2-18

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在 MATLAB Online 中打开

You try to visualize the contours of a 2 x 2 image. That should most likely look degraded. And note that for the values chosen each row is simply 1/10 of the previous row:

F(b+1, r) = F(b, r)/10

Is this correct?

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Answer 2

Walter Roberson 2013-2-16

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Why are you trying to pass 6 parameters in to contour()? contour expects at most 4 numeric parameters (excluding name/value pairs)

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Walter Roberson 2013-2-17

Have you tried restarting MATLAB? Then put in a breakpoint at the meshgrid line, and examine the size() and print the values of the variables to see how many entries show up and what they are.

Kelly 2013-2-17

I have, and the size() is the same, but the values print as 1x4 like they are supposed to do, and the computations are correct. I checked them by hand.

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Answer 3

Image Analyst 2013-2-17

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https://ww2.mathworks.cn/matlabcentral/answers/63742-trying-to-plot-a-radial-contour#answer_75343

I'm not really sure I follow what you're trying to do, nor do I know what sort of output ratio_rp_bf() creates, but if you just want to draw dircles, see the FAQ:

http://matlab.wikia.com/wiki/FAQ#How_do_I_create_a_circle.3F

If F is an image that you created that's supposed to be a circular cone so that contours on it would be concentric circles, then please upload that image since I don't have ratio_rp_bf() which creates it.

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Kelly 2013-2-17

在 MATLAB Online 中打开

%this is the function the main program is calling to run all the computations F, for the length of bD, using R and theta which are dependent variables and which vary directly.

function F = ratio_rp_bf(R,theta,bD)

for r = 1:length®

for b = 1:length(bD)

F(b,r) = (16/3).*(1./bD(b)).*(1./R(r)).^3.*abs(sqrt((1./R(r)).^4-2.*(1./R(r)).^2.*cos(2.*theta(r))+1));

end

% This is the main program. After all the computations have been done, the output should be a 2x2 contour subplot in the form of a circle for each bD. The bD should cause a break to form in the plotted circle.

bD = [0.1, 1.0, 10, 100];

R = (1:1.25:5);

c = R;

a = 1/2*bD;

b = abs(sqrt(c.^2 - a.^2));

theta = abs(atan(b./a)); %finds the angle theta for each given radii (R)

[F] = ratio_rp_bf(R,theta,bD);% calls function to perform computaions

              for b = 1:length(bD)
               figure(1)
               subplot(2,2,b)
               x = R.*cos(theta); % conversion from polar coordinates to cartesian.
               y = R.*sin(theta);
               z = (x.^2+y.^2)<=R.^2;
               [C,h] = contour(x,y,z,F);
               clabel(C,h);
               grid on
  end

I get an error stating z needs to be size 2x2 or greater.

Kelly 2013-2-17

According to my professor, contour(R,theta,bD) should plot the contours of the expression F and it should be radial with breaks at each bD.

Walter Roberson 2013-2-18

One of you has misinterpreted. The three-argument form of contour() is always X, Y, Z coordinates. To use specific contour levels, you need the two-input or four-input forms of contour(). See http://www.mathworks.com/help/matlab/ref/contour.html

Note that you have not included F in your contour() call.

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