How to change the value of a variable every iteration?

Hi all,

I want to change the value of 'trip_duration' every iteration. I have the following code:

maxtime=120
threshold_temperature=30
for i=1:maxtime
  trip_duration=i
  for t=1:120; %iteration over all values 1-120 
      current_temperature =temperature_hourly(t,:); %where 'temperature_hourly' reads in one value from a text file until the 120th value
      if  current_temperature <= threshold_temperature 
          Influenceof_temp_current= 1;
      else
          Influenceof_temp_current = current_temperature/threshold_temperature;
      end
      time_since_last_water = trip_duration*(Influenceof_temp_current) ;
      prob_drinking = 1/(1+exp(-.05*(time_since_last_water-10)));
      rn=rand;
      if prob_drinking>rn
          k=1;
      else
          k=2;
      end
  end
end

The issue that I am having is that trip_duration does not change with every iteration, where my intention is for trip_duration to be 1 when i=1, 2 when i=2, etc. Consequently, the outputs for 'prob_drinking'are not correct. The error that I am receiving is "Attempted to access trip_duration(2); index out of bounds because numel(trip_duration)=1." If I simply run the first "for" loop, 'trip_duration' changes as I need it to, but not if I run the whole code (where it is always 120). Any ideas as to why this is occuring?

Thanks in advance

[Geoff Hayes]

Stephanie - you may need to provide more details. When I run the above code, I see that trip_duration increments for each iteration of the outer for loop. Or are you expecting it to increment for all iterations of the inner for loop instead?

[Stephanie Diaz]

Hi Geoff, Sorry if I repeat myself because I'm not sure how best to describe this. The purpose of the inner for loop is to read in values 1 to 120 of a text file for iterations 1 to 120 of the outer for loop. So, value 1 of the text file will be read in for i=1, and value 2 will be read in for i=2, etc.'Trip_duration' should be equal to i, but would it not be the same if it incremented in the inner for loop, given that the inner for loop is for 1:120 (and 120 is the maxtime for the outer loop). I hope this makes sense.

[Stephanie Diaz]

I think I may have fixed this. All that I did was make trip_duration equal to t in the inner for loop. Not too sure why this solved my problem though!

[KL]

if you replace trip_duration with t, what's the point of the outerloop? Probably you wouldn't need it, at least for this snippet of code

[Adam]

You don't appear to be storing or outputting any results from either loop so what exactly is the expected final result of all this?

You say trip_duration is always 120, but when is 'always'? How are you determining what it's value is? Are you stepping through a breakpoint 14400 times?!

[Stephanie Diaz]

This is part of a larger script, and the reason for the two for loops is to read in "t" from a text file such that one value is read in every "i" until maxtime. I wasn't sure how else to portray this w/o two for loops, although Adam, I see what you're saying and I definitely do not want 14400 iterations!