Question

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 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”…

Answer 1

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.