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Fitting a curve in log-linear plot.

Sat, 11/19/2011 - 04:16 am

Hi all,

I want to fit a curve through 6 points (please see figure attached, the curve in the picture is a drawn one not a fitted one. That is just to give a feel how the fitted curve would look like.) in a log-linear plot. Is there any way I can do it in igor? Thanks.

yaohualiu

Hi, Igor Magician:

You need to know the relationship between the two variables to fit the data. It does not matter how the data are displayed.

Click the menu "Analysis:Curve Fitting...". You will see a popup window. Click "new fit funtion" under the tab "Function and Data" to define you own fitting function. It is pretty straitforward then. Click "Help" button there if you need more help.

Yaohua

November 19, 2011 at 06:49 pm - Permalink

johnweeks

I don't think you really want to "fit a curve". You probably want a spline curve or bezier curve. Since your curve is not a function (there are places where it has multiple Y values for a given X value), you will probably have to draw it by hand using Igor's drawing tools.

I think the log axis may cause problems, too. I would make a new X wave containing log(x) and plot on a linear axis. Then use Igor's drawing tools to create a bezier curve.

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com

November 21, 2011 at 09:14 am - Permalink