How to plot a 3D surface with two vectors and one array?

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I want to plot a 3D surface , but I cannot apply the surf() command straightforwardly for some reason.
I have two vectors for x and y coordinates. Let us say
x = linspace(-10, 10, 100);
y = linspace(-0.5, 0.5, 100);
To calzulate I have to call some function which works only for fixed values of x and y. Thys, I calculate it as follows
for i = 1 : length(x)
for j = 1 : length(y)
func(i,j) = @MyFunction(__some_parameters__, x(i), y(j));
end
end
As a result I have two vectors for x and y and a matrix of the size length(x)*length(y) for the variable z. Could you tell me please, if there are any convenient methods to rewrite this data to a format that is appropriate for applying the surf() command?
P.S. I used plot3(x(i), y(j), func(i,j), 'b.') with two cycles, but it is a ridiculous "dirty hack" and not a surface.

Accepted Answer

Walter Roberson
Walter Roberson on 21 Oct 2021
Create full vectors of coordinates and arrayfun()
x = linspace(-10, 10, 100);
y = linspace(-0.5, 0.5, 100);
[X, Y] = meshgrid(x, y);
Z = arrayfun(@(xx,yy) sin(xx)+atan2(yy,xx), X, Y);
surf(x, y, Z, 'edgecolor', 'none')
  3 Comments
Bogdan MP
Bogdan MP on 22 Oct 2021
Well, it looks like I can simply write
surf(x, y, z')
Walter Roberson
Walter Roberson on 22 Oct 2021
surf(x, y, z')
If that worked for your purposes, then chances are that when you constructed z, you varied x values down columns, and that you varied y values across rows -- that array z(J,K) is a function of x(J), y(K) . That is a very common data organization... but it is not the MATLAB data organization. In MATLAB, up/down (so, along columns) is y, and left/right (so, along rows) is x, and array location z(J,K) is z(y(J), x(K)) .
When you use meshgrid(xvector, yvector), then the coordinates are arranged in such a way that surf(x, y, z) works out.
When you use ndgrid(xvector, yvector) then the coordinates are arranged in such a way that surf(x, y, z) errors (unless xvector and yvector are the same length).
xvec = 1:2; yvec = 1:3
yvec = 1×3
1 2 3
[X, Y] = meshgrid(xvec, yvec)
X = 3×2
1 2 1 2 1 2
Y = 3×2
1 1 2 2 3 3
[X, Y] = ndgrid(xvec, yvec)
X = 2×3
1 1 1 2 2 2
Y = 2×3
1 2 3 1 2 3

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