What are practical uses for STL's 'partial_sum'?

Question

What/where are the practical uses of the partial_sum algorithm in STL?

What are some other interesting/non-trivial examples or use-cases?

Answer 1

One thing to note about partial sum is that it is the operation that undoes adjacent difference much like - undoes +. Or better yet if you remember calculus the way differentiation undoes integration. Better because adjacent difference is essentially differentiation and partial sum is integration.

Let's say you have simulation of a car and at each time step you need to know the position, velocity, and acceleration. You only need to store one of those values as you can compute the other two. Say you store the position at each time step you can take the adjacent difference of the position to give the velocity and the adjacent difference of the velocity to give the acceleration. Alternatively, if you store the acceleration you can take the partial sum to give the velocity and the partial sum of the velocity gives the position.

Partial sum is one of those functions that doesn't come up too often for most people but is enormously useful when you find the right situation. A lot like calculus.