How to create custom Mesh for PDE model

Hi:

I want to create a custom mesh for a 2D PDE model different from the one that 'generateMesh' creates automatically. Following examples, I have defined the geometry, edges information, nodes, triangle elements, etc. I am only using only a single rectangular structure. But when I try to assign my mesh info to my model directly, like:

 MyCustomMesh= pde.FEMesh(MyNodesMatrix,MyTriangleElements,#max,#min,'linear', --> ??? <---);

that last parameter is required, but there is no info at all about it in the documentation. Whenever you look for the pde.FEMesh properties, all that you get listed is:

 - Properties for class pde.FEMesh:
 *     Nodes
 *     Elements
 *     MaxElementSize
 *     MinElementSize
 *     GeometricOrder

because inside the FEMesh.m function you have:

 classdef (Sealed) FEMesh  < handle
 properties(SetAccess=private)    
    Nodes;
    Elements; 
    MaxElementSize;  
    MinElementSize;
    GeometricOrder;    
  end

properties(Hidden=true)   
  MeshAssociation;      
end

 methods
    function [p, e, t] = meshToPet(obj)

        p = obj.Nodes;
        if obj.MeshAssociation.PetFormat
            e = obj.MeshAssociation.EdgeAssociativity;
        else
            e = obj.MeshAssociation;
        end        
        t = obj.Elements; 
        if size(p,1) == 2
            t(end+1,:) = obj.MeshAssociation.RegionAssociativity;
        else
            t(end+1,:) = ones(1,size(t,2));        
        end
    end   
  end
  methods(Hidden=true)   
    function obj=FEMesh(nodes, elems, maxelemsz, minelemsz, order,assoc)
        obj.Nodes = nodes;
        obj.Elements = elems;
        obj.MaxElementSize = maxelemsz;
        obj.MinElementSize = minelemsz;
        obj.GeometricOrder = order;
        obj.MeshAssociation = assoc;   
    end   
  end 
end

'MeshAssociation' is hidden, and the function caption doesn't give any description like it does for all other properties. Yet the last parameter is required. I would like to see my mesh plotted to verify it, but I cannot get to the point of running

 MyCustomMesh= pde.FEMesh(MyNodesMatrix,MyTriangleElements,#max,#min,'linear', --> What goes here? <---);
 model.Mesh=MyCustomMesh;
 pdeplot(model);

because I get

 Error in pde.FEMesh/meshToPet (line 69)
        if obj.MeshAssociation.PetFormat

What are the alternatives for 'PetFormat', or how is it supposed to be defined as the required last parameter? Or is there a different way to assign a custom mesh to a PDE structure (+2015a). I don't want to use legacy [p,e,t] format if possible, unless it is the only alternative.

Thanks.

Answer 1

[Alan Weiss]

I think that you can create your own mesh as long as you stick with the following two rules:

• Don't use a PDEModel to represent your problem
• Represent your boundary conditions using a boundary file or a boundary matrix exported from the PDE app.

Then, as long as you have a consistent [p,e,t] representation of your mesh, I believe that solvers will be able to use your custom mesh.

Good luck,

Alan Weiss

MATLAB mathematical toolbox documentation

[amir13631363]

Hi Alan: I have a 3D mesh data and I want to calculate [p,e,t]. I should impose my boundary condition for a part of the face (not the whole of it). Could you please guide me how could I define the boundary (e) for the 3D problems. Bests, Amirreza