View, Edit, and Delete PDE Coefficients

View Coefficients

A PDE model stores coefficients in its EquationCoefficients property. Suppose model is the name of your model. Obtain the coefficients:

coeffs = model.EquationCoefficients;

To see the active coefficient assignment for a region, call the findCoefficients function. For example, create a model and view the geometry.

model = createpde();
geometryFromEdges(model,@lshapeg);
pdegplot(model,'FaceLabels','on')
ylim([-1.1,1.1])
axis equal

Specify constant coefficients over all the regions in the model.

specifyCoefficients(model,'m',0,'d',0,'c',1,'a',0,'f',2);

Specify a different f coefficient on each subregion.

specifyCoefficients(model,'m',0,'d',0,'c',1,'a',0,'f',3,'Face',2);
specifyCoefficients(model,'m',0,'d',0,'c',1,'a',0,'f',4,'Face',3);

Change the specification to have nonzero a on region 2.

specifyCoefficients(model,'m',0,'d',0,'c',1,'a',1,'f',3,'Face',2);

View the coefficient assignment for region 2.

coeffs = model.EquationCoefficients;
findCoefficients(coeffs,'Face',2)

ans = 
  CoefficientAssignment with properties:

    RegionType: 'face'
      RegionID: 2
             m: 0
             d: 0
             c: 1
             a: 1
             f: 3

This shows the "last assignment wins" characteristic.

View the coefficient assignment for region 1.

findCoefficients(coeffs,'Face',1)

ans = 
  CoefficientAssignment with properties:

    RegionType: 'face'
      RegionID: [1 2 3]
             m: 0
             d: 0
             c: 1
             a: 0
             f: 2

The active coefficient assignment for region 1 includes all three regions, though this assignment is no longer active for regions 2 and 3.

Delete Existing Coefficients

To delete all the coefficients in your PDE model, use delete. Suppose model is the name of your model. Remove all coefficients from model.

delete(model.EquationCoefficients)

To delete specific coefficient assignments, delete them from the model.EquationCoefficients.CoefficientAssignments vector.

coefv = model.EquationCoefficients.CoefficientAssignments;
delete(coefv(2))

Tip

You do not need to delete coefficients; you can override them by calling specifyCoefficients again. However, deleting unused assignments can make your model smaller.

Change a Coefficient Assignment

To change a coefficient assignment, you need the coefficient handle. To get the coefficient handle:

• Retain the handle when using specifyCoefficients. For example,

  coefh1 = specifyCoefficients(model,'m',m,'d',d,'c',c,'a',a,'f',f);

• Obtain the handle using findCoefficients. For example,

  coeffs = model.EquationCoefficients;
  coefh1 = findCoefficients(coeffs,'face',2);

You can change any property of the coefficient handle. For example,

coefh1.RegionID = [1,3];
coefh1.a = 2;
coefh1.c = @ccoeffun;

Note

Editing an existing assignment in this way does not change its priority. For example, if the active coefficient in region 3 was assigned after coefh1, then editing coefh1 to include region 3 does not make coefh1 the active coefficient in region 3.

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