How to plot all values of a variable that changes?

I have some code where x starts off at some number and then is either divided by 2 or multiplied by 3 and then added to 1. This goes on until x=1. I need to keep track of every value that x was in order to reach 1.

Answer 1

[Star Strider]

This assumes ‘x’ begins as greater than one and will stop when it is less than or equal to one (taking into account floating-point-approximation error):

k1 = 1;
while x > 1
    ... CODE ...
    x_sav(k1) = x;                  % Save Each Value OF ‘x’
    k1 = k1 + 1;
end

Save ‘x’ in a separate vector after you have calculated it in each iteration of the loop.

[Bryce Kuhn]

This is the code I'm using. I've used something similar to record iterations

   clear
    x = input('What is the last three digits of your student number? ')

    it=0

    while x>1 

   if mod(x,2)
    x=x*3+1
    it=it+1;
   else
    x=x/2

    it=it+1;
   end

    end

    plot(x,it)
    display 'The number of iterations ='
    disp(it)

[Star Strider]

If I understand correctly what you want to do, you need at some point in the loop (probably after the if block) to save the value of ‘x’ as (for example):

x_sav(it) = x;

Note that you are not saving incremental values of ‘it’ but only the last value.

The plot would then be:

plot([1:it], x_sav)

assuming you want to plot ‘x’ as a function of the iterations. (I put square brackets [] around the iteration vector because I know by looking then that it is a vector. This makes the code easier for me to read. They are not necessary for the code.)

[Bryce Kuhn]

Wow this worked great! Thanks!

[Star Strider]

My pleasure!

You did all the heavy lifting — I just tweaked your code a bit to save your iterative ‘x’ values.