Another option is to enter equations in the weak form using the Weak Contribution node (). This can be convenient in advanced modeling because it controls the test variables multiplying the equations. Wherever a test function of a dependent variable appears (in the Global Equations node or elsewhere in the model), whatever it multiplies ends up in the same equation in the discrete system. To add a Weak Contribution, either right-click The Global ODEs and DAEs Interface and select it from the context menu or click Weak Contribution on the toolbar.

Enter the expression that contains the weak formulation in the Weak expression field.