Question

following problem: Having a base triple (0,1,0)

Now I try to create a list of changed triples in a given range.

The constraints:

1. triple[0] and triple[2] have should have a maximum of r, such as r=0.2
2. sum(triple) = 1
3. triple[0] needn’t to be equals triple[1] and should be increased by a given stepwise-parameter s, such as s= 0.02

In this above mentioned example our methode should create

lst = [(0.0, 1, 0.0),(0.02, 0.98, 0.), (0.04, 0.96,0), (0.04,0.94, 0.02), (0.06,0.94,0), (0.06, 0.92, 0.02), (0.06, 0.9, 0.04), ...]

Is there any pretty way to do this?

Maybe you have an idea to create these list without nested loops (probably with numpy?).

Thanks a lot!

Answer 1

Here’s a list comprehension that should provide all 3-tuples that meet your constraints (as I understand them). Its a bit more clunky than I’d like due to the range function only accepting integers:

r = 0.2
s = 0.02
steps = int(math.ceil(r/s))
lst = [(a*s, 1-(a+b)*s, b*s) for b in range(steps) for a in range(steps)]

Results:

>>> lst[0:4]
[(0.0, 1.0, 0.0), (0.02, 0.98, 0.0), (0.04, 0.96, 0.0), (0.06, 0.94, 0.0)]
>>> lst[90:94]
[(0.0, 0.8200000000000001, 0.18), (0.02, 0.8, 0.18), (0.04, 0.78, 0.18), (0.06, 0.76, 0.18)]

The first and last values only go up to 0.18 in this code, and I’m not sure if that’s desirable or not (is the constraint < r or <= r?). It shouldn’t be too hard to tweak, if you want it the other way.