# Graphing in Cylindrical Coordinates using MATLAB

Asked by Mark on 29 Apr 2012
Latest activity Commented on by Geoff on 3 May 2012

Hello,

I want to reproduce this graph... http://i45.tinypic.com/121xra1.jpg ... using MATLAB.

It's the graph of g(r, theta) = 1 + r^2*sin(theta) over the unit circle.

Thanks :)

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Answer by Geoff on 30 Apr 2012

Advice is to make a start and show us what you have done so far.

Here is my primer:

r = 0:0.1:1;
theta = linspace(0, 2*pi, 12);


You need to use meshgrid

doc meshgrid


And surf

doc surf


And a polar co-ordinate conversion

<insert high-school trigonometry>


The colour map is jet.

I think that's plenty to get you started =)

Geoff on 3 May 2012

And one last hint on camera placement. Look at the line on the mesh that appears to be vertical. You want your camera rotated to that point, and you need to experiment with the tilt to get the right elevation. Standard isometric view used by engineers. It'll be an obvious angle.

Mark on 3 May 2012

I've got it to this:

r=0:0.1:1;
theta=linspace(0, 2*pi, 13);
[r,theta]=meshgrid(r,theta);
x=r.*cos(theta);
y=r.*sin(theta);
z=1+r.^2.*sin(theta);
mesh(x,y,z)
grid on
axis tight
view([300,30])
xlabel('x = r cos(\theta)')
ylabel('y = r sin(\theta)')
zlabel('g(r,\theta)')
title('Question 6(b)')

the only thing I can see that needs changing the the scaling on the axes

Geoff on 3 May 2012

Really?

I can see:

- Axis tick labels (and number of grid guides) not consistent with example;

- Colour of grid guides not consistent with example;

- Aspect ratio of default figure not consistent with example;

- Anti-aliasing of mesh lines not consistent with example;

- Background colour of figure not consistent with example.

I pointed out some of these things before. Aren't you lucky to stumble across a fussy old bugger like myself to make your life difficult =)