How to remove a single point from meshgrid?
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I have written this code and want to model the temperature profile. I want to exclude (0,0) from the meshgrid as the function becomes infinite there. How can I do that?
x = linspace(-3,10);
y = linspace(-3,0);
zero_x_idx = find(x == 0);
zero_y_idx = find(y == 0);
% Exclude the point (0, 0) from the arrays
x = x([1:zero_x_idx-1, zero_x_idx+1:end]);
y = y([1:zero_y_idx-1, zero_y_idx+1:end]);
[X,Y] = meshgrid(x,y);
Z=(P_l*exp(-v(sqrt((X.*10^(-3)).^2 + (Y.*10^(-3)).^2) + (X.*10^(-3)))/(2*a)))/(4*3.14*k*sqrt((X.*10^(-3)).^2 + (Y.*10^(-3)).^2))+T0;
1 Comment
Answers (2)
I would use ‘logical indexing’ to simply delete that point —
x = linspace(-3,10)
y = linspace(-3,0)
x = x(x~=0)
y = y(y~=0)
Another option would be to replace it with something small, however not zero —
x = linspace(-3,10)
y = linspace(-3,0)
x(x==0) = NaN
y(y==0) = NaN
x = fillmissing(x, 'nearest')
y = fillmissing(y, 'nearest')
The second approach sets the zero value equal to NaN, and then interpolates it with the nearest (most likely non-zero) value.
.
4 Comments
AD
on 31 Jul 2023
Star Strider
on 31 Jul 2023
Edited: Star Strider
on 31 Jul 2023
The problem is here:
Z=(P_l*exp(-v(sqrt((X*10^(-3)).^2 + (Y*10^(-3)).^2) + (X.*10^(-3)))/(2*a)))/(4*3.14*k*sqrt((X*10^(-3)).^2 + (Y*10^(-3)).^2))+T0;
↑ HERE
It needs to be:
Z=(P_l*exp(-v.*(sqrt((X.*10^(-3)).^2 + (Y.*10^(-3)).^2) + (X.*10^(-3)))./(2*a)))./(4*pi*k*sqrt((X.*10^(-3)).^2 + (Y.*10^(-3)).^2))+T0;
instead.
There is a missing operator of some type (I assume multiplication). I also did element-wise division everywhere, sincer that is usually overlooked and I assume that here you would want to do it.
x = linspace(-3,10);
y = linspace(-3,0);
x(x==0) = NaN;
y(y==0) = NaN;
x = fillmissing(x, 'nearest');
y = fillmissing(y, 'nearest');
[X,Y] = meshgrid(x,y);
P_l = randn;
v = randn;
a = randn;
k = randi(10);
T0 = randn;
Z=(P_l*exp(-v.*(sqrt((X.*10^(-3)).^2 + (Y.*10^(-3)).^2) + (X.*10^(-3)))./(2*a)))./(4*pi*k*sqrt((X.*10^(-3)).^2 + (Y.*10^(-3)).^2))+T0;
figure
contourf(X, Y, Z)
That worked correctly when I ran it.
EDIT — (31 Jul 2023 at 17:21)
.
AD
on 31 Jul 2023
Star Strider
on 31 Jul 2023
My pleasure!
First, notice that zero doesn't appear in x:
x = linspace(-3,10);
zero_x_idx = find(x == 0);
zero_x_idx
But if you used different endpoints or a different number of points in linspace, zero might appear:
x = linspace(-3,10,131);
zero_x_idx = find(x == 0);
zero_x_idx
So, I'm going to go with that.
(Zero does appear in y):
y = linspace(-3,0);
zero_y_idx = find(y == 0);
zero_y_idx
Second, notice that removing the 0 from x and the 0 from y before using them in meshgrid removes not only the point (0,0) but also the lines x=0 and y=0 from the X and Y matrices returned by meshgrid. In other words, you'll have the situation where X and Y don't have any points where X is 0 or Y is 0, instead of the situation where X and Y don't have any points where X is 0 and Y is 0. (I'm sure you've noticed this already but were not sure how to remove a single point instead of both lines, hence the question.)
Here's one way to remove the single point (0,0) from X and Y:
[X,Y] = meshgrid(x,y);
% note: X,Y includes (0,0) at this point in the code:
[r0,c0] = find(X == 0 & Y == 0)
% create a logical matrix of which points to keep:
to_keep = true(size(X));
% set the element at zero_y_idx,zero_x_idx to false:
to_keep(zero_y_idx,zero_x_idx) = false;
% only keep the points in X and Y where to_keep is true:
X = X(to_keep);
Y = Y(to_keep);
% sanity check: that (0,0) is gone
[r0,c0] = find(X == 0 & Y == 0)
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on 31 Jul 2023
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