3D plotting of equation

Hi! I need to plot such an equation (function) in 3D space:

2*x^2+1.5*x*y-.8*x*z+2.5*y^2-3*y*z+z^2-0.35=0.

Everything that I have found, the function is

   f(x,y,z)=... or f(x,y)=... .

I tried to use

v=2*x^2+1.5*x*y-.8*x*z+2.5*y^2-3*y*z+z^2;
scatter3(x(:), y(:), z(:), [], v(:));

and slice v=0.35, but turns out only x, y and z could be sliced.

Thank you very much in advance.

Answer 1

[Walter Roberson]

 syms x y z
 f = 2*x^2+1.5*x*y-.8*x*z+2.5*y^2-3*y*z+z^2-0.35;
 fimplicit3(f, [-2 2 -2 2 -2 2])

[samira karimi]

Thank you so much. This is exactly what I have been looking for, for 3 whole days!

[samira karimi]

Another question; is there any way to plot a volume of f<=0 instead of just f=0?

[Walter Roberson]

You can use

   f = 2*x^2+1.5*x*y-.8*x*z+2.5*y^2-3*y*z+z^2-0.35 <= 0

with the fimplicit, but for reasons unknown you end up with a chunkier version of the same output when you would expect the same output instead, since <= 0 would just be the filled version of the shape.