CODEWITHSUNDEEP
matlab
Sean M.
Sean M.

Reputation: 593

Plot gradient of a function which is a matrix in MATLAB

I would like to plot the gradient of the following function in MATLAB.

g(x,y) = [(x^2)-1; -y]

My code is:

x = linspace(-3,3);
y = linspace(-3,3);
[xx, yy] = meshgrid(x,y);
z = [xx.^2-1;-yy];
[dx,dy] = gradient(z,.3,.3);
contour(x,y,z)
hold on 
quiver(x,y,dx,dy)

But I'm just getting this error:

The size of Y must match the size of Z or the number of rows
of Z.

I've no idea how I could make the size of both match. y is a 1x100 matrix and z a 200x100. To match them I would need y to be a 1x200 or z to be 100x100, but would I be able to plot it then?

Upvotes: 2

Views: 2444

Answers (1)

RussH
RussH

Reputation: 341

Instead of

z = [xx.^2-1;-yy];

try each component separately:

z1 = [xx.^2-1];
z2 = [-yy];
[dx,dy] = gradient(z1,.3,.3);
contour(x,y,z1)
%etc.

Use hold on again if you really want them in the same plot.

Upvotes: 2

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