My plot wont show up in the plot window.

First off I left out some of the code because I want to focus on only Newtons method part of this. With inputs 1,2,0.75,0.001,30 I get the right values out but when the plot window comes out it doesn't show anything. I've tried setting up a zeroes array but the values wont go into the array. Any tips on how to fix this?

 function [ ] = Project1(nFunction, nMethod, x0, epsilon, nStop)
f1 = @(x) x.^3-3*x.^2+3*x-1;
df1 = @(x) 3*x.^2-6*x+3;
f2 = @(x) tan( x );
df2 = @(x) sec( x ).^2;
f3 = @(x) x+cos(x) .* exp(-50*x.^2);
df3 = @(x) 1-exp(-50*x.^2).*(100*x*cos(x)+sin(x));
n=0;
    if ( nFunction == 1 )
        f=f1;
        xs=1;
    elseif ( nFunction == 2 )
        f=f2;
        xs=pi;
    else
        f=f3;
        xs=-0.1832913;
    end;

    if ( nMethod == 1 )
        bisection( f );
    elseif ( nMethod == 2 ) 
        if ( nFunction == 1 )
            df=df1;
        elseif ( nFunction == 2 ) 
            df=df2;
        else
            df=df3;
        end
        newton( f,df );
    else
        secant( f );
    end
function [] = newton( f ,df ) 
while(abs(xs-x0)> epsilon && n <= nStop); 
    n=n+1;
    x = x0-f(x0)/df(x0);
    x0=x;    
    disp( sprintf( 'Approximate using Newtons = %e', x ));
    disp( sprintf( 'Error = %e', xs-x0 ));
    semilogy( n, f(x), 'b-');
end
end
end

Answer 1

[Walter Roberson]

Add

hold on

after the semilogy() call

[Sean Poitou]

It changed the axis numbers to something that looks more reasonable but still no line. :\

[Walter Roberson]

Of you want a line you need to plot more than one point at a time. Matlab does not join points in different plotting calls. Make a vector of results and plot the vector