Hanna L. Dolin

            function threeEx()
%matlab code for Collatz Conjecture 3n+1 Problem
%This script assumes the Collatz Conjecture holds,
%that sequences end in the 421 loop

start=input('Enter vector of starting values (+ real integers) []: ');
    if start<=0
        start(start<=0)=input('Replace start<=0 with + real integers []:');
         %correct terms if input wrong  
         newvec=sprintf('%d ',start);
         fprintf('Starting values: %s ',newvec)
    end

peak=[];
%initialize vector of max. values
labcol='rgbcmykw';
%start condition
    for i=1:length(start)
        %assign starting position
        val=[start(i)];
        while val(end)~=1
         %Assuming all + real integers result in end sequence 421
            if rem(val(end),2)==0
             val=[val val(end)/2];
            else
             val=[val 3*val(end)+1];
            end
        end
        %build values for results of operation on starting value
    hold on
        if i<=length(labcol)
         lincol=strcat('-',labcol(i));
        elseif rem(i,length(labcol))==0
         lincol=strcat('-',labcol(end));
        else
         lincol=strcat('-',labcol(rem(i,length(labcol))));
        end
    %Assign plot colors
    plot(1:length(val),val,lincol)
    %plot values
        for x=1:length(val)
         text(x+.05,val(x),num2str(val(x)))
        end
    %label each point
    peak=[peak max(val)];
    %Find max value of sequence
    end
peak=sprintf('%d ',peak);
fprintf('Max value(s): %s\n',peak)
%output max values of sequences associated with starting values
end