# Discrete inequality plotting

I have an equation like this: $${20 \choose k}\cdot \sum_{i=0}^k {k \choose i}\cdot i \leq 1+f$$.

I want to plot this inequality as the dependency between k and f. I found a commend RegionPlot but I don't know how to correctly use it in such equation.

• You have an inequality, not an equation. :) – Svend Tveskæg Dec 9 '13 at 13:58
• @SvendTveskæg Yes, you are right ^^ – Ziva Dec 9 '13 at 15:32

ListPlot[Table[{k, Binomial[20, k] Sum[i Binomial[k, i] - 1, {i, 0, k}]}, {k, 1, 20}], Filling->Top] Or the same using a Log scale If you want only integer values you can put k in Round:

RegionPlot[Binomial[20, Round[k]] Sum[
i Binomial[Round[k], i], {i, 0, Round[k]}] <= 1 + f, {k, 1, 20}, {f, 0, 5 10^9}] Your function is explicit, so it will be better to use ListPlot as in belisarius's answer:

ListPlot[Table[{k - 0.5, Binomial[20, k] Sum[i Binomial[k, i], {i, 0, k}] - 1}, {k, 20}],
Filling -> Top, Joined -> True, InterpolationOrder -> 0] Also one can note that

Sum[i Binomial[k, i], {i, 0, k}]

 2^(-1 + k) k


The inequality you are considering is simplified as follow.

Consequently, we can use RegionPlot easily.

2^(-1+k) k Binomial[20,k]<=1+f
RegionPlot[2^(-1+k) k Binomial[20,k]<=1+f, {k,-4,10},{f,-20,40}] 