Contour plot not working (but contour3 plot does work)

2013 7 26
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Hello everyone,
For some reason when I use the 'contour' function, it just gives me a blank figure. On the other hand, if I use 'contour3' it displays the 3-D contour plot. Any suggestions why this may be happening?
I have a 31x1 double (x-axis), a 19x1 double (y-axis), and a 31x19 double (z-axis).
- First, I use meshgrid with the x and y-axis, which gives me a 19x31 and 19x31 respectively.
- Next, I transpose the z-axis to obtain a 19x31 (just as the other 2 axis)
- Finally, I plot them and obtain the desired surface and mesh plots; but, I am unable to obtain the contour plot as I mentioned above.
Thank you in advance for any help provided.

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David (degtusmc)
David (degtusmc) 2013-9-5

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I am still not sure why the 'contour' function did not work for me. It must be some bug in my code.
I ended up using the 'contour3' function. To obtain the regular contour, I use the 'rotate 3D' toolbar and by right clicking on the plot it gives the option to "Go to X-Y view" which is the regular contour.

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Richard McCulloch
Richard McCulloch 2013-7-27

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From my understanding, meshgrid will create a matrix out of x and y to provide a 2 dimensional indexing for z. To get a simple 2D contour the vectors have to be the same size. This is because you are essentially defining a z value at an ordered pair (x,y). If the data is linear maybe look at linspace to make them all the same length.

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David (degtusmc)
David (degtusmc) 2013-7-29
Thank you Richard for the answer. After I use meshgrid and I transpose the z-axis, all of them are 19x31.
Richard McCulloch
Richard McCulloch 2013-7-29
Is your Z a single value? I am getting it to work fine with this example:
x=[1:31]'; y=[1:19]'; z=rand(31,19);
size(x), size(y), size(z)
ans =
31 1
ans =
19 1
ans =
31 19
[x,y]=meshgrid(x,y);
contour(x,y,z')
contour3(x,y,z')
Are any errors showing up? This is a unique problem it seems.
Richard
David (degtusmc)
David (degtusmc) 2013-8-1
To be completely honest I am not sure what is wrong with it. No errors are showing up and both surface and mesh plots work fine with the same data.
The weirdest part is that, when I went to check if any errors were showing, I commented out the 'contour3' function and replaced it with the regular 'contour' function. I ran it, and it worked!!! Then I deleted the 'contour3' (commented line) and ran it again, but this time it did not work and it has not work since then.
Thanks for the help though.

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