plot smooth CDF using matlab

I would like to make the curve smoother, how is that possible?

       clear all; close all;
  y = [0.75862069 0.666666667 0.882352941 0.875   0.736842105 0.566666667 0.703703704 0.6 0   0.730769231 0.714285714 0.625   0.675   0.693877551 0.731707317 0.558823529 0.679245283 0.740740741 0.785714286 0.789473684 0.615384615 0.6 0.739130435 0.576923077 0   0.75];
  cdfplot(y)

plot image -> http://i.stack.imgur.com/Gy9IW.jpg

[Wayne King]

Are you sure that you want to "smooth" an ECDF? I don't think that's a good idea. The ECDF inherently has a staircase appearance and smoothing it distorts the purpose of the ECDF.

What are you trying to gain by smoothing the ECDF?

[Dror Dayan]

trying to do a theoretical cdf, to explain a behaviour and not actual data.

Answer 1

[Wayne King]

You could do something like this:

         [f,xi] = ksdensity(y);
         y1 = cumsum(f);
         y1 = y1./max(y1);
         x = (1:100)/100;
         plot(x,y1,'k','linewidth',2);
         hold on;
         cdfplot(y);

By using ksdensity() to esimate the density.

[Dror Dayan]

the problem with that its not accurate enough at the beginning x < 0.2

Answer 2

[Wayne King]

That is because the ECDF necessarily jumps, you could just use ecdf()with confidence bounds

    [F,X,Flo,Fup] = ecdf(y);
    plot(X,F); 
    hold on;
    plot(X,Flo,'r-.'); plot(X,Fup,'r-.');

will be smoother than

stairs(X,F);