Replacing for loop in order to decrease run time

I'm trying to add the difference between 2 arrays (if A(i) > B(i)) to the next element of array A. I'm unsure how to decrease the time needed to run this code (it'll be integrated using ode45)

for i = 1:length_chain_classes
    if Rate_array(i) > ChainLengths(i)                      %% if more glucose gets designated to class than it can accept, at surplus to next class
        Surplus_g1p = Rate_array(i) - ChainLengths(i);
        Rate_array(i) = ChainLengths(i);
        if i ~= length(Rate_array)                             %% voids surplus only if at last class
            Rate_array(i+1) = Rate_array(i+1) + Surplus_g1p;
        end  
    end
end

I'm unsure how to reference the next/previous value in a vector without using a for loop

[Tommy]

It seems like the order in which this loop runs does matter, as you might change Rate_array(i+1) on one iteration, thereby changing the result of Rate_array(i) > ChainLengths(i) on the next iteration. Therefore, vectorizing this code may leave you with incomplete results. You could solve the issue by rerunning the code until you know you're done, demonstrated below using sample A and B vectors:

A = randi(10,10,1);
B = randi(10,10,1);
i = A>B;
while any(i)
    sg = A-B;
    A(i) = B(i);
    A([false; i(1:end-1)]) = A([false; i(1:end-1)]) + sg([i(1:end-1); false]);
    i = A>B;
end

There may be a better way. This at least shows how you can "reference the next/previous value in a vector without using a for loop."

[Bastiaan]

Thanks! This code seems to improve the performance by a bit

Answer 1

[Athul Prakash]

Hi Bastiaan,

I think this way you can solve it. Below is how yo

D = A(1, end-1) - B(1, end-1);
D = [0; D]      % ';' Assuming A & B are col vectors. Otherwise use ','
A = A + D;

Hope it helps!