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In what contexts do programming languages make real use of an Infinity value?

Asked 2008-12-19T23:54:04.747
28

So in Ruby there is a trick to specify infinity:

1.0/0
=> Infinity

I believe in Python you can do something like this

float('inf')

These are just examples though, I'm sure most languages have infinity in some capacity. When would you actually use this construct in the real world? Why would using it in a range be better than just using a boolean expression? For instance

(0..1.0/0).include?(number) == (number >= 0) # True for all values of number
=> true

To summarize, what I'm looking for is a real world reason to use Infinity.

EDIT: I'm looking for real world code. It's all well and good to say this is when you "could" use it, when have people actually used it.

python ruby language-agnostic idioms infinity
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4 Answers

11

In some physics calculations you can normalize irregularities (ie, infinite numbers) of the same order with each other, canceling them both and allowing a approximate result to come through.

When you deal with limits, calculations like (infinity / infinity) -> approaching a finite a number could be achieved. It's useful for the language to have the ability to overwrite the regular divide-by-zero error.

answered 2008-12-20T00:07:03.100
8

Alpha-beta pruning

answered 2008-12-20T00:46:51.770
3

I've used it in the minimax algorithm. When I'm generating new moves, if the min player wins on that node then the value of the node is -∞. Conversely, if the max player wins then the value of that node is +∞.

Also, if you're generating nodes/game states and then trying out several heuristics you can set all the node values to -∞/+∞ which ever makes sense and then when you're running a heuristic its easy to set the node value:

node_val = -∞
node_val = max(heuristic1(node), node_val)
node_val = max(heuristic2(node), node_val)
node_val = max(heuristic2(node), node_val)
answered 2008-12-22T13:56:57.557
1

When working in a problem domain where trig is used (especially tangent) infinity is an answer that can come up. Trig ends up being used heavily in graphics applications, games, and geospatial applications, plus the obvious math applications.

answered 2008-12-20T00:01:33.140

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