Taking a value of a specific time

[Hossein]

Dear Tom, Administrator,

I want to make a comparision between two consecutive value by IF THEN ELSE function. Then, I need to take these values and compare. Somthing like the following example.
IF THEN ELSE (value at Time i = value at Time i+1, 0, value at Time i+1 - value at Time i)

Could you please help me?
BR,

[Hossein]

I just solved it by constituting Time i+1 via DELAY FIXED function by one unit. Afterward, I deducted the two variables and it works! However, is there another direct solution?

[Administrator]

I just solved it by constituting Time i+1 via DELAY FIXED function by one unit. Afterward, I deducted the two variables and it works! However, is there another direct solution?

This is the correct way to do it.

[Hossein]

Dear Tom, Administrator,

I want to get the value of the first time of a flow and use it as the initial value of its level (please see the attached figure) i. e. I want to use the value of "Emission rate" at the first time as the initial value of "Total emission". Could you please help?

BR,

[Administrator]

This should work, have you tried it?

total emissions = integ ( emissions rate, emissions rate).

[Hossein]

Dear Administrator,

Thanks for your reply.
Actually, I did not try it because I thought since emission rate is changing, the initial value of total emission would also change! However, now, I tried it and worked!
Thanks again.

[tomfid]

Setting

Total Emissions = Emissions Rate

is dimensionally inconsistent (TonC vs. TonC/year, for example).

You probably want to include some kind of time constant on the right hand side, so for example

Total Emissions = Emissions Rate*Initial History Duration
Initial History Duration = 1 year (or whatever).