How can I do an calculation where it uses the previous answer to calculate the next

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rammah nagi 2019-8-6

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评论： rammah nagi 2019-8-6

Twout.PNG

So I want to model how a water tank changes in temperature when water is put in. So my Tank is 3600 L capacity and the flow into the water is 360 L/hr. If the water temperatre at the start is 290 Kelvin and the water temperature entering over 24 hours is as follows:

So this is what i need to do.

(3600*Tt+360*Twout/(3600+360)) %where Twout is as shown in the picture 
%Tt is the variable that changes every hour so for the first hour Tt is equal to 290, but in the second hour it is equal to (3600*Tt+360*Twout)/ and so on for 24 hours

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Renato SL 2019-8-6

From what I understand:

Tt0 is known (your example is 290).
Tt1 = 3600*Tt0 + 360*Twout(1) / (3600 + 360)
Tt2 = 3600*Tt1 + 360*Twout(2) / (3600 + 360), and so on

Is this it?

rammah nagi 2019-8-6

Yes this would work, i was just wondering whether there is a method that would do it without having to write all lines.

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Answer 1

Renato SL 2019-8-6

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I would do something like this

Tt = 290; %temperature at the start
for i=1:24 %loop for 24 hours
    temp = (3600*Tt(end) + 360*Twout(i)) / 3960; %basically, your formula
    %Tt(end) to call the last value of Tt which is the result of the last computation
    %Twout(i) for corresponding Twout value
    Tt = [Tt temp]; %updating the value of Tt with the value of the last computation
end

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Renato SL 2019-8-6

Actually, please recheck the formula since the one that you write basically makes the value goes to infinity

temp = 3600*Tt(end) + 360*Twout(i) / (3600+360);
%basically temp = 3600*Tt (adds a minimum of 4 digits to the value) + a small addition

so that in my answer I put the brackets to the addition before the division

temp = (3600*Tt(end) + 360*Twout(i)) / (3600+360);
%so that temp = (hundreds of thousands) / (thousands)
%        temp = a value in hundreds

I don't know the exact formula so please don't just use what I put as the answer.

rammah nagi 2019-8-6

I used what you did earlier and it seemed to work just fine, i get very realisitic results

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How can I do an calculation where it uses the previous answer to calculate the next

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