What is wrong with this while loop

I have written a long-ish function, it says "busy", heats up the computer, and does not finish even if I reduce the size of the arrays involved drastically. When I ctrl+C it, it always terminates on a while statement, or the if statement nested inside it, or the "end" for those 2.

This is the code, with the while loop and if statement written in full:

for t=2:(totaltime/timestep)

      <stuff, including arraysize(t)=arraysize(t-1)>

      for i=1:arraysize(t-1)
          <lots of stuff, including increasing arraysize(t) - I thought the issues would crop up here>
      end

      n=(0.1/60)*timestep*currentcells(t-1);
      while remcells(t)<n
              r=randi(arraysize(t));   %line 108
              if yeast.biomass(t,r)>0   %line 109; yeast.biomass is an array of size arraysize(t), I'm picking n random elements from it
                  remcells(t)=remcells(t)+1;
                  currentcells(t)=currentcells(t)-1; % I thought it was a potential problem but removing it made no difference
                  <some undemanding stuff>
              else
                  continue
              end
      end
      <very undemanding stuff>
  end

Given that whenever I terminate it, it ends at that same line

"Operation terminated by user during timevolution (line 108)"

(More usually) "Operation terminated by user during timevolution (line 109)"

I assume there's something wrong with that while loop or the if statement. Is there? Or does it ending at that same line not mean anything?

Any help will be greatly appreciated! I am a novice at Matlab (and coding in general) so if there's something "obvious" that might be a solution please point it out...

[Walter Roberson]

What evidence is there that yeast.biomass(t,r)>0 for any r ? Or that n is not Very Big ?

[Saaz Sakrikar]

yeast.biomass is initialised at 1 for all yeast and is an exponentially growing function I only set it =-10^-6 to mark a yeast I want to remove.

n should be a small fraction of the size of the array yeast.biomass, so I don't think that should be a problem either.

I will check both of those out though, thanks for the advice. If that's going wrong there are deeper problems in my model!

Answer 1

[Star Strider]

I can’t run your code, so these are wild guesses. There are two possibilities that I see:

First, see what the end condition for the for loop is, specifically the value of (totaltime/timestep). The default increment is 1 for colon-operator vectors. The end condition value could be larger than you thought.

Second, check the value of ‘yeast.biomass(t,r)’ is to be certain you enter the if block. Write the values of ‘n’ and ‘remcells(t)’ to the Command Window within your while loop. The while condition might never be satisfied.

These are where I would look.

[Saaz Sakrikar]

I don't think the totaltime/timestep is a problem, I used a siplified version of this code with the same loop and had no problems.

I will check the remcells by making n = 1 and seeing if the code responds.

[Star Strider]

It’s best not to take anything for granted. Check everything — the values of all variables — that might be a part of this problem.