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paripari-gp

How to determine which numbers lie within a certain range

I currently have a list of numbers, and I want to know which of these numbers are within a certain range, and what their position is in the list.

I'm reasonably new to pari so I'm not sure how exactly to go about this.

For a simplistic example of what I'm doing:

Find the inverses of the numbers 1 to 20 which lie within the range 0.05 and 0.15

I've set up a list like this:

A=[1/i|i<-[1..20]];

From here, I'd like a list of all the i so that A[i] is in that range.

But I'm not sure how to proceed from here. I tried some simple if/for statements, but these weren't working.

How exactly would I try and go about something like this?

Solution

  • You want to use select: Either:

    select(i->A[i]>=0.05 && A[i]<=0.15, [1..#A])

    Or more compactly using the flag 1 to return indices:

    select(v->v>=0.05 && v<=0.15, A, 1)