Differential Function

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Level 1

15 points

Differential Function

Hello,

I'm having trouble writing a differential function. I have a number of variables (S, Re and Rr) and a set of values (labelled t), 1-10 for instance. I would like to write the following formula in Numbers:

It = (It-1+Re*S) - (It-1*Rr) (please note, the t and t-1 notation is in subscript).

I can't understand how to represent It-1 in Numbers? Any help would be appreciated,

Barry

MacBook, Mac OS X (10.5.6)

Posted on Jul 29, 2010 6:46 AM

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Answer 1

Jul 29, 2010 8:59 AM in response to Barry Shortt

Barry Shortt wrote:
I can't understand how to represent It-1 in Numbers? Any help would be appreciated,

Barry,

The answer depends on how the data in your table is arranged. I assume that your "It-1" refers to the prior value of "I". You will simply have to reference the most recent value; i.e., "It" is the current value of I and "It-1" is the value of "I" just prior to this one.

The reason you will have to be careful is that you have to decide how to treat the calculation for time 1, or not make a calculation for that time, because the derivative isn't defined at the boundary.

Jerry

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