Question

How do I create a function of a list, such that if any member of the list is negative it is zero, otherwise it follows a recursion relation.

Mathematically this is what I have to do, but I’m not sure how to do it in Mathematica.

Thanks.

Edit: To be completely precise, I am trying to implement the recursion relation on page 6 of this paper (eq 18):
http://arxiv.org/PS_cache/nlin/pdf/0003/0003069v1.pdf

However, it’s quite complicated and requires a fair amount of reading to understand, so I didn’t want to bring it into the question!

Answer 1

Testing if any member of a list satisfies some condition can be done using MemberQ. To test if the list lst contains any element less than zero,

lst = {1, 2, 0, -4};
MemberQ[lst, x_ /; x < 0]

The second argument here is a conditional pattern.

But yes, knowing what it is you want to do would help.