# Numerically integrate a function whose lower limit depends on a parameter?

GROUPS:
 I have a function f(r) that I want to integrate numerically. The code is NIntegrate[f[r], {r, lowerlimit[r], Infinity}] . The lower limit is given by lowerlimit=c if r<=100 and lowerlimit=2*r otherwise, note that r can not be negative and c is some positive number. I wonder how to implement this integral.
14 days ago
5 Replies
 This doesn't make any sense. You appear to be using the name r to refer to the variable of integration as well as an independent parameter. Please be clearer.
14 days ago
 On your paper, you have x as the variable of integration, which makes sense. Do that in your code. Define your function lowerlimit using Piecewise, Condition, or even If. Then your expression will, given a value for r, yield a result.