A problem drawing a graph in matlab

I'm trying to draw a graph of density in matlab and I'm encountering several problems.

First, binValues is a function that does this :

(for example:)

binValues([24767 33119 30397 31150 26729 29446 28574 29085]',4)
ans =
24767 26855 2
26855 28943 1
28943 31031 3
31031 33119 2

here n = 4, number of categories. In the code at the bootom n=3.

This is the code that doesn't work well:

function graph = histogram(z,n)
data = binValues(z,n); % 
z=sort(z);

sum=0;
for i=1:n
    sum=sum+data(i,3);
end
density = zeros(n,1);
for i=1:n
    density(i)=(data(i,3))/(sum);
end

dens=zeros(1,length(z));
for j=1:length(z)
    for i=1:n
        if (z(j)>data(i,1)) && (z(j)<=data(i,2))
            dens(j)=density(i);
        end
    end
end

      y = zeros(1,2*length(z));
      xnew = zeros(1,2*length(z));

      xnew(1) = z(1);
      xnew(2) = z(1);
      y(1) = 0;
      y(2) = dens(1);

for i=2:length(z)
        xnew(2*i-1) = z(i);
        xnew(2*i) = z(i);
        y(2*i-1) = dens(i-1);
        y(2*i) = dens(i);
end

graph = plot(xnew,y);

end

When I run it for histogram([1 2 2 1 1 1 3 3 2 2 2 1 1 1 4]',3), the plot seems to be biased to the right. It suupose to be like the one on the left, see here : http://oi48.tinypic.com/os4j7d.jpg

Any ides what's the problem? I'm not allowed in this exercise to use other functions besides plot,xlim,ylim,min and max.

Thank's!

[googo]

Any problem with the question? I truly need your help. Thank you very much.

Answer 1

[Doug Hull]

Why not use the built in hist command in MATLAB to get a histogram?

[googo]

I'm not allowed to use this. Looking at the code and the result i'm not far away but something is definitely wrong. ======================================================= ok... I think I fix it... it was suppose to be *if (z(j)>=data(i,1)) && (z(j)<data(i,2))*

Any ideas how to normalize this histogram, so it will be a probability density function? And how do i find what is the surface under the graph?