fitting data to a known equation curve

[Carmen]

Version: 2008
Operating System: Mac OS X 10.5 (Leopard)
Processor: Intel

I'm using Excel 2008 for Mac and I'm wondering how I can fit some data to a curve of known equation to obtain the fitting coefficients. The equation is exponential (y=a*((1+b*exp(-0,26*x)) but not that one Excel uses when you choose exponential fitting.
Is there any way of introducing the formula to get the fitting coefficients a and b?

 

[Carl Witthoft]

Version: 2008
Operating System: Mac OS X 10.5 (Leopard)
Processor: Intel

I'm using Excel 2008 for Mac and I'm wondering how I can fit some data to a
curve of known equation to obtain the fitting coefficients. The equation is
exponential (y=a*((1+b*exp(-0,26*x)) but not that one Excel uses when you
choose exponential fitting.
Is there any way of introducing the formula to get the fitting coefficients a
and b?

It's not all that hard in Excel, but you really Reeeeely will be
happier if you switch to a genuine stats/analysis package to do work
like that.
Also, you need to rewrite your equation so it has independent
coefficients: y = A' + B'*exp(-0.26*x) {if you absolutely MUST have
your a and b, just back-plug them after completing the curve fit}

Back to Excel: one of the simpler ways is to create a column with the
values exp(-k*x) . call that column's values z for clarity:

Then do LINEST(y,z)

Or, just take my modified equation there and play with LOGEST a little.