Index out of bounds error

I'm trying to simulate random protein production and degradation. I want it so that only one of those 3 outcomes can occur in any one loop. I keep getting this error though:

_Attempted to access N(1248); index out of bounds because numel(N)=1247.

Error in Assignment_2 (line 11)
    p2 = DegradationRate*DeltaTime*N(n-1);_

Every time I run the program, the error is at different values. Here is my code so far:

clear
N0=0; 
DegradationRate = 0.01;
ProductionRate = 1;
DeltaTime = 0.1;
MaxTime=500;
N(1)=N0; 

for n = 2:(MaxTime/DeltaTime+1)
    p1 = ProductionRate*DeltaTime;
    p2 = DegradationRate*DeltaTime*N(n-1);
    pRandom = rand(1);
        if pRandom < p1
            N(n)=N(n-1)+1;
        end

          if p1 <= pRandom < p2
              N(n)=N(n-1)-1;
          end

          if (p1+p2) < pRandom
              N(n)=N(n-1);
          end

end

Time = 0:DeltaTime:(MaxTime/DeltaTime);
plot(Time,N,'r')

I tried my best to play around with it, but I can't seem to get rid of that error. Any help will be appreciated!

Answer 1

[Walter Roberson]

If none of the three "if" conditions hold then you do not assign to N(n). You also have not preallocated N, which you should do for efficiency.

Part of your problem is that p1 <= pRandom < p2 does not do what you think it does. It means ((p1 <= pRandom) < p2) where the (p1 <= pRandom) returns a logical vector (0 and 1). Change your code to

if (p1 <= pRandom) & (pRandom < p2)

[Musa]

Thank you very much!