Z must be a matrix, not a scalar or vector.

Hello,

I would like to turn the figure drawn by this code:

t = linspace(-10,10,1000);
xt = exp(-t./10).*sin(5*t);
yt = exp(-t./10).*cos(5*t);
p = plot3(xt,yt,t);

Which gives this

To a figure with a filled surface, like one can do with surf, like so:

[X,Y] = meshgrid(1:0.5:10,1:20);
Z = sin(X) + cos(Y);
surf(X,Y,Z)

But,

surf(xt,yt,t);

gives this error: "Z must be a matrix, not a scalar or vector."

Thanks for your support

Answer 1

[Just Manuel]

Well, have a look, what X, Y and Z are that allow you to make a surface.

Meshgrid gives you matrices for X and Y, thus Z is also a matrix (20 by 19 in your example).

You need to specify height values in t, so express it as a function of X and Y.

Cheers

Manuel

[Just Manuel]

Try something along the lines of

[X,Y] = meshgrid(-2:0.2:2,-2:0.2:2);
[phi,r] = cart2pol(X,Y);
Z = -10.*log(r);
surf(X,Y,Z)

Which yields this:

Or even better: use the approach from this answer:

https://ch.mathworks.com/matlabcentral/answers/53954-how-do-you-create-a-surf-plot-in-cylindrical-coordinates

r = 0.5:0.1:2;
phi = 0:0.1:2*pi;
[R,PHI] = meshgrid(r,phi);
Z = -10.*log(R);
surf(R.*cos(PHI), R.*sin(PHI), Z)

Which yields this:

And please accept the answer, if it was of use to you.

Cheers

Manuel

[AYMERIC BARBIN]

Thanks !