How can I improve performance via a high-level approach when implementing long equations in C++

Question

I am developing some engineering simulations. This involves implementing some long equations such as this equation to calculate stress in a rubber like material:

Answer 1

It looks like you have a lot of repeated operations going on.

pow(l1 * l2 * l3, -0.1e1 / 0.3e1)
pow(l1 * l2 * l3, -0.4e1 / 0.3e1)

You could pre-calculate those so you are not repeatedly calling the pow function which can be expensive.

You could also pre-calutate

l1 * l2 * l3

as you use that term repeatedly.