MATLAB: How to plot a quadratic equation

3d plotsplottingsurface

Hello everybody!

I've been struggling with this for a while and I don't know how to do that..

I would like to plot this: x²+y²+z²-2xy-4x+4y-1=0

thanks for your help!

Hello,

If you have a newer release of Matlab (I believe R2016b), you can use the new fimplicit3 function,

fimplicit3(@(x,y,z) x.^2+y.^2+z.^2-2*x.*y-4*x+4*y-1)

which will default to plotting on the interval [-5,5] (for all axes) but you can change this interval with the second input argument.

Hope this helps!

Two options:

1. Set Z > 4 to NaN:

[X,Y] = meshgrid(-5:.2:5);                                
Z = -0.15*sin(X).*(X) + 0.2*(Y.^2) +3 ;
Z(Z>4) = NaN;
figure
surf(X,Y,Z)

2. Use a zlim cutoff:

[X,Y] = meshgrid(-5:.2:5);                                
Z = -0.15*sin(X).*(X) + 0.2*(Y.^2) +3 ;
figure
surf(X,Y,Z)
zlim([min(zlim) 4])

There may also be other possibiloities.

Did you look up ellipsoid in the help? When or if you do, you'll find your answer with very very slight modifications to their demo:

[x, y, z] = ellipsoid(0,0,0, 2,3,1, 30);
surfl(x, y, z)
colormap copper
axis equal