View, Edit, and Delete Initial Conditions

View Initial Conditions

A PDE model stores initial conditions in its InitialConditions property. Suppose model is the name of your model. Obtain the initial conditions:

inits = model.InitialConditions;

To see the active initial conditions assignment for a region, call the findInitialConditions 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

Figure contains an axes object. The axes object contains 4 objects of type line, text.

Specify constant initial conditions over all the regions in the model.

setInitialConditions(model,2);

Specify a different initial condition on each subregion.

setInitialConditions(model,3,Face=2);
setInitialConditions(model,4,Face=3);

View the initial condition assignment for region 2.

ics = model.InitialConditions;
findInitialConditions(ics,Face=2)

ans = 
  GeometricInitialConditions with properties:

           RegionType: 'face'
             RegionID: 2
         InitialValue: 3
    InitialDerivative: []

This shows the "last assignment wins" characteristic.

View the initial conditions assignment for region 1.

findInitialConditions(ics,Face=1)

ans = 
  GeometricInitialConditions with properties:

           RegionType: 'face'
             RegionID: [1 2 3]
         InitialValue: 2
    InitialDerivative: []

The active initial conditions assignment for region 1 includes all three regions, though this assignment is no longer active for regions 2 and 3.

Delete Existing Initial Conditions

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

delete(model.InitialConditions)

To delete specific initial conditions assignments, delete them from the model.InitialConditions.InitialConditionAssignments vector.

icv = model.InitialConditions.InitialConditionAssignments;
delete(icv(2))

Tip

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

Change an Initial Conditions Assignment

To change an initial conditions assignment, you need the initial conditions handle. To get the initial condition handle:

Retain the handle when using setInitialConditions. For example,
```
ics1 = setInitialConditions(model,2);
```
Obtain the handle using findInitialConditions. For example,
```
ics = model.InitialConditions;
ics1 = findInitialConditions(ics,Face=2);
```

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

ics1.RegionID = [1,3];
ics1.InitialValue = 2;
ics1.InitialDerivative = @ut0fun;

Note

Editing an existing assignment in this way does not change its priority. For example, if the active initial conditions in region 3 was assigned after ics1, then editing ics1 to include region 3 does not make ics1 the active initial condition in region 3.