Code initiates again after exiting while loop which is within an if statement

i = 2
for i = 2:523
    if Storage(i-1) >= Stage_1_trigger
        Outflow = Demand_and_losses
        if Storage(i-1) + Flow(i) - Outflow < 0
            Storage(i) = 0
        elseif Storage(i-1) + Flow(i) - Outflow > Initial_storage
            Storage(i) = Initial_storage
        else
            Storage(i) = Storage(i-1) + Flow(i) - Outflow
        end
        Storage(i)
        i = i + 1
    else 
        while Storage(i-1)<= Stage_1_exit
        Outflow = 0.9*Demand_and_losses
        
            if Storage(i-1) + Flow(i) - Outflow < 0
                Storage(i) = 0
            elseif Storage(i-1) + Flow(i) - Outflow > Initial_storage
                Storage(i) = Initial_storage
            else
                Storage(i) = Storage(i-1) + Flow(i) - Outflow
            end
            i = i + 1
        end 
    end
end

Hi, I have this code above. However, when the code exits the while loop, the i value initiates again.

For example, before entering the while loop, i = 5. When exiting the while loop, i = 10. However, when the code finishes with the while loop and goes back to the first for loop, i = 5 again rather than 10. How can I prevent this? Thanks!

Answer 1

[Bjorn Gustavsson]

In your outer for-loop you use you use i as loop-index. The way matlab has implemented things this is done (IIRC) such that there will be an array with loop-index-values that the loop-variable will step through. This has precedence, so this differs from for example C where the loop simply increments until the interrupt-condition. You might have to code this differently.

First time you fall into the while-loop you will start with some value of i, lest say 5, it will be incremented to 10, then next time through the for-loop i will be set to the next value of the index-array, i.e. 6, and then proceed with that.

The simplest way to implement this snippet to behave in the C-way might be to change the outer for-loop to a while-loop and just make sure the incrementing of i behaves as you want.

HTH

[Arielle Patapanian]

Thanks, I got it to work by changing the outer loop from a for loop to a while loop like you suggested!

Answer 2

[Walter Roberson]

I gave a detailed explanation of how for loops work in https://www.mathworks.com/matlabcentral/answers/356884-how-do-i-convert-this-for-loop-into-a-while-loop#answer_281739

[Arielle Patapanian]

Thanks for the help!