Using Matlab for solving 3d PDE and creating geometry

Hi I need to solve a 3D diffusion equation on a geometry of a sphere inside a cube.

However - I saw that in PDE toolbox I can only create a sphere inside a sphere or a cube inside a cube. Therefore I would like to ask:

1. How can I create this kind of geometry?
2. How would I then manage the boundary conditions?
3. What is the right syntax for coefficient speficiation in 3D (speficially here the sphere is a source and the cube has no source)?

Thanks.

[sevgi]

hello, I have a similar problem. did you find a solution

Answer 1

[Ravi Kumar]

Here is an example.

gmCube = fegeometry(multicuboid(1,1,1));
gmCube = gmCube.translate([0,0,-0.5]); % Translate so that the cube is centered at the origin.
gmSphere = fegeometry(multisphere(0.25));
gmSphereInCube = addCell(gmCube,gmSphere);
pdegplot(gmSphereInCube,'CellLabels','on','FaceAlpha',0.5)

If you are using MATLAB R2022b or older, then skip the fegeometry() calls.