plotting cumulative distribution function

Question

c = 2;
P = N[n*Log[n]]
K = N[c*Log[n]]

Needs["PlotLegends`"];

PrDEqK[P_, K_, n_, c_, k_] := Module[{p, q, r, ps, qs, m, tmp},
    r = Sqrt[(c*Log[n])/(n*\[Pi])];
    p = \[Pi]*r^2;
    q = 1 - p;
    ps = 1 - Binomial[P - K, K]/Binomial[P, K];
    qs = 1 - ps;

   N[Sum[Binomial[n - 1, m]*p^m*q^(n - 1 - m)*Binomial[m, k]*ps^k*
      qs^(m - k), {m, k, n - 1}]]

   ];
Plot[CDF[{PrDEqK[P, K, 20, c, k], {k, 1, 8},Filling -> Axis
]

i'm not getting the CDF plot...what is the problem?

Answer 1

As has been CDF acts on distribution objects. You have defined a discrete PMF. With all due respect the plot by Boson is not a CDF but a continous plot of PMF.

Reproduing user-defined:

c = 2;
n = 20;
P = N[n*Log[n]];
K = N[c*Log[n]];

PrDEqK[P_, K_, n_, c_, k_] := 
  Module[{p, q, r, ps, qs, m, tmp}, r = Sqrt[(c*Log[n])/(n*\[Pi])];
   p = \[Pi]*r^2;
   q = 1 - p;
   ps = 1 - Binomial[P - K, K]/Binomial[P, K];
   qs = 1 - ps;
   N[Sum[Binomial[n - 1, m]*p^m*q^(n - 1 - m)*Binomial[m, k]*ps^k*
      qs^(m - k), {m, k, n - 1}]]];

To generate CDF:

cdf[k_] := Sum[PrDEqK[P, K, 20, c, j], {j, 0, k}];

Visualizing:

DiscretePlot[cdf[k], {k, 0, 8}]

Answer 2

I tried to clean your code a little and it worked right away:

c = 2;
n = 20;
P = N[n*Log[n]];
K = N[c*Log[n]];

PrDEqK[P_, K_, n_, c_, k_] := 
  Module[{p, q, r, ps, qs, m, tmp}, r = Sqrt[(c*Log[n])/(n*\[Pi])];
   p = \[Pi]*r^2;
   q = 1 - p;
   ps = 1 - Binomial[P - K, K]/Binomial[P, K];
   qs = 1 - ps;
   N[Sum[Binomial[n - 1, m]*p^m*q^(n - 1 - m)*Binomial[m, k]*ps^k*
      qs^(m - k), {m, k, n - 1}]]];

Plot[PrDEqK[P, K, n, c, k], {k, 1, 8}, Filling -> Axis]

EDIT: I am sorry, I have not read the question thoroughly and did not notice you wanted a CDF. ubpdqn is absolutly right.