How to do simple Boltzmann fit on a graph ?

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I know it should be simple to do but I am quite novice with Igor. I have to fit simple conductance of INa curve measured from an IV protocol.

The equation what I have to use is:

g/gmax = ((A1-A2)/(1+exp(-(E-Ehalf/k))+A2

Thank you in advance for help.
If you haven't done it yet, you should look at the Getting Started help, including doing the at least the first half of the Guided Tour.

For this problem, you need to create a user-defined fit function. You can read about that in the Curve Fitting help. Copy this command, paste it into Igor's command line and press Enter:

DisplayHelpTopic "Fitting to a User-Defined Function"

But I would suggest reading from the start of the Curve Fitting help file.

Note that you will need to multiply through by gmax; you can only have the dependent variable on the left side of the equation you're fitting.

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com

January 12, 2015 at 09:28 am - Permalink

Dear Dr. Weeks,

Thank you for your reply. It was really useful.
I also would like to fit data points with a parabolic function: Variance = q*I-(1/N)*I^2
I would like to ask how can I "force" the fit to start from zero?

Best regards,

mrtanki

March 9, 2015 at 07:29 am - Permalink

Do you have a data set with Variance as the dependent variable? And is I the independent variable? In that case, if you create a user-defined fitting function that implements your equation, it will automatically pass through the origin.

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com

March 10, 2015 at 01:20 pm - Permalink