Let consider the geometry of a brushless motor (picture below) on which one would like to compute the magnetic force on the boundary composed of the lines L1, L2 and L3.
In Flux2D, this computation is performed using line integral following the procedure below:
1  From menu Advanced, select Integral of a spatial quantity>Integral on line 

2  In the displayed window:

The same computation is done automatically using the macro CreateSensorFor2DMotorSlotForce available on Altair connect.