Function Design

I have an array contanining the position of the different objects in my scene. To calculate the next movement step

I want to build a function like this:

f(x) = 1/(x-pos1)^2 + 1/(x-pos2)^2 + ...
       ^term1         ^term2         ^term_n

I don't know how many objects are in my scene so I want to add terms in the function for each objects:

something like:

for object in scene:
     add_one_term_to_the_function
return function

is there a way to program this? Preferably 开发者_开发知识库in C++ or Python... the only two languages I know...

PS: thx for the answers... but a loop is not what I'm looking for. This would be extremly slow.. because it will calculate the function everytime I call a next event... but I want to calculte it only once... and then pass the events to the calculated "function"...

---

Why not loop over them? It's not going to be very much slower than otherwise.

def f(x,poslist):
  v = 0
  for pos in poslist:
    v += 1/((x-pos)*(x-pos))
  return v

If you really want to do it in python you can do it like this (but I beleive it's going to be very slow)

def addterm(f, pos):
  def g(x):
    return f(x)+1/((x-pos)*(x-pos))
  return g

def zero(x): return 0
f = zero
for pos in poslist:
  f=addterm(f, pos)

There is no real analogue in C++, because C++ doesn't have closures. One could simulate it, but it won't be the same, and then you could use a list and a loop instead anyway.

---

function = lambda x : sum([1/(x-obj.pos)**2 for obj in scene])

then you can do

function(10);function(100); (and so on)

---

Sure, just use a container and a loop:

#include <vector>
#include <cmath>

double f(double x, const std::vector<Position> & positions)
{
  double res = 0;
  for (std::vector<Position>::const_iterator it = positions.begin(); it != positions.end(); ++it)
  {
    res += std::pow(x - *it, -2);
  }
  return res;
}

I assume that Position is a type that's convertible to a floating point number. You pass a collection of positions as the second argument to the function. std::vector is the prototypical container in C++, but there are others to choose from if you have specific needs.