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Exponential regression

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Dear all, So sorry for pestering you like this. i am trying to solve an equation: I = (0.5)+A(1-e^(BV)) (0.5) is a constant - it won''t vary, but i''m still not sure what it is yet, about 0.5 i should say I know three points on the curve, and i need to regress in real time... I know I and V values. How would i go about regressing it? What steps should i take? (ps. this is not homework... again, it''s for my solar car group. Sorry it''s not game related, but this is the best forum for "coding maths" that i know of. ) Cheers, JB

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You could probably do a least squares regression. You can look up the closed form solution of the exponential least squares regression on mathworld.

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is there any other way to do it beside least squares least squares is slow :I

Because i know the form , shouldn''t you be able to work it out??

Cheers,
JB

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Of course I could work out the closed form, but why bother fight the lack of mathematics symbols posting it in text when mathworld has it all pretty like?

And probably least squares is as fast it gets as long as you''re trying to model an exponential function.

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The way I would do it would be to transform the data points such that they are linear, do a linear least squares regression, and then undo your transformation on the least squares equation and you''ll have an exponential function that reasonably models your data. I don''t know if this is faster then using a closed form exponential least squares regression, but the math may be simpler..

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maybe im an idiot, but i think you havnt fully explained what your problem is.

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Hi,

Thanks, i know you can do it with least squares, but that takes time to solve. Is there some other way to solve it?

I''ll re-state my problem if u don''t get it:

I = (0.5)+A(1-e^(BV))

I know I and V, (3 sets of data points) and i want to find A and B.

CHeerZ, JB

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What range and precision needed? I remember you saying something in that other thread about this being on some dinky 8-bit micro - does it have enough memory (or eprom-access-capability) to use a lookup table?

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only if its smaller than 256 bytes. i have a full c compiler that will compile for it

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wouldnt two sets of I and V be enough?

that would give you two equations and two unknown, otherwise youre just overdefining the problem, or am i still missing something?

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