# Differentiating potential energies

1. Jan 18, 2008

### Edcellence

I've read a paper titled "A Versatile and Robust Model for Geometrically Complex Deformable Solids"

Can someone familiar with numerical computations and mechanics help me understand this paper?

A deformable body is discretized in tetrahedron elements.

In equation (2), the force for a mass point is a derivative of its potential energy:

F = -k*C*$$\frac{\partial C}{ \partial p _{i}}$$

where k is the stiffness coefficient and C is the potential energy.

I am not sure how the force of a mass point $$p_{i}$$
can be computed. What does it mean by differentiating with respect to a point $$p_{i}$$?