Seemingly the same inputs into a PLCM function, different outcomes?

Wendy

2013 3 20

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I wrote a function which worked as the Piecewise Linear Chaotic Map——PLCM which perform the following task: Xn+1=F(Xn,p)= 0<=Xn<p: Xn+1= Xn/p P<=Xn<0.5: Xn+1= (Xn-p)/(0.5-p); 0.5<=Xn<1: Xn+1= F(1-Xn,p). p=0.2

 function [outnum] =PLCM(innum,p)
    if(innum>=0&&innum<p)
         outnum=innum/p;
    end
    if(innum>=p&&innum<0.5)
        outnum=(innum-p)/(0.5-p);
    end
    if(innum>=0.5&&innum<(1-p))
        outnum=(1-innum-p)/(0.5-p);
    end
    if(innum>=(1-p)&&innum<=1)
        outnum=(1-innum)/p;
    end
end

The input X0=0.1 and X0=0.9, the result turn out as

PLCM(0.9,0.2) ans = 0.5000 >> PLCM(ans,0.2) ans = 1.0000 >> PLCM(ans,0.2) ans = 1.6653e-015

PLCM(0.1,0.2) ans = 0.5000 >> PLCM(ans,0.2) ans = 1 >> PLCM(ans,0.2) ans = 0 >> PLCM(ans,0.2) ans = 0

After the first round,the ans seem to be the same, but why the same input result in different outputs? Has anyone ever faced such problems? Or is it concerns to the inner computing method of Matlab??