My graph in matlab has a blank strip in the middle

i graphed the following

if true
  % code
end[x,y]=meshgrid(-1:.01:1, -1:.01:1);
a = .619211.*x.^2;
b = (53913.*x.^8.*y.^2 + 2560.*x.^6);
c = 232.192.*(b).^1/2;
d = (c - 53913.*x.^4.*y).^1/3;
e = a./d;
f = (53913.*x.^8.*y.^2 + 2560.*x.^6).^1/2;
g = 232.192.*f;
h = (g - (53913.*x.^4.*y));
i = .0011982.*[(h).^1/3];
z = e - i;
surf(x,y,z);shading interp

and now my graph has a strip running through the middle that is blank. how do i get rid of it/fix it

Answer 1

[John D'Errico]

dpb is close, but not quite there.

The problem is when x == 0. Look at your code, line by line, thinking about what happens. (This is how you should debug these issues, and it took me far less time to resolve the issue than it took me to write this response.)

When x == 0, we see that a == 0.

Likewise, when x == 0, b == 0, and therefore c == 0.

And if you look at d, clearly when both c and x are zero, it too will be zero.

So now look at e. What is 0/0? NaN. And NaNs are like rabbits - they propagate.

Therefore, when x == 0, you get z == 0 along that line.

The trivial fix is to avoid having x == 0. So instead of having a spacing of 0.01, which gives you an odd (201) number of points over the interval [-1,1], use exactly 200 points.

[x,y]=meshgrid(linspace(-1,1,200));

The disfiguring line of NaNs will now be gone.

[Nismeta]

thank you!

Answer 2

[dpb]

z(isnan(z))=0;
surf(x,y,z)

I didn't look to see which term precisely causes the problem but you've got a numerical issue somewhere that's giving a row of nan for y=0 I believe it is.

[Joseph Cheng]

I think its is actually when x=0 is where it Nan. If we go back to your original question. and look where these equations come from

http://www.mathworks.com/matlabcentral/answers/uploaded_files/15756/doc1.pdf there are the equations shown when x~=0. Are there modifications to the equation for when x=0? or specific equations for when x does = 0;

[Nismeta]

Here is the equation i used for this graph. it is the first z = one. i found this equation when i scrolled down the page. i have tried fixing all the numerical errors and i can't see any new ones.