function v=collatziter(s,t,myfl);
%s=value to test, t=no. of iterations, myfl 0=plot vals 1= web plot
%Example collatziter(-17,50,1)
%process stop and reports when it reaches a period
clf;
%upper=6;
steps=t;
w=1;
res=200;
%xi=zeros(1,steps);
xi(1)=s;
mymax=s;
mymin=s;
i=2;
flag=0;
while (i<=steps)&(flag==0)
    xi(i)=myfn(xi(i-1));
    if xi(i)>mymax
        mymax=xi(i);
    end
    if xi(i)<mymin
        mymin=xi(i);
    end
    j=i;
    while (j>1)&(flag==0)
        j=j-1;
        if xi(j)==xi(i)
            flag=1;
        end
    end 
    i=i+1;
end
its=i-1;
if myfl 
    steps=i-1;
    x=zeros(2*steps-2);
    y=x;
    for i=w:steps-1
        y(2*i-1)=xi(i+1);
        y(2*i)=xi(i+1);
        x(2*i-1)=xi(i);
        x(2*i)=xi(i+1);
    end
    hold on
    xx=linspace(mymin,mymax,res);
    yy=myfn(xx);
    plot(xx,yy,'y');
    yy=xx;
    plot(xx,yy,'g');
    line(x,y);
else
    plot(xi);
end
   
hold off
for i=w:its
        fprintf('%2.0f \n',xi(i));
end
fprintf('Steps=%2.0f \n',steps);
fprintf('Period=%2.0f \n',i-j);

function myval=myfn(x)
two=x;
for i=1:length(x)
    two(i)=2;
end
myval=(two+7*x-(two+5*x).*cos(pi*x))/4;