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Pressure-Volume Curve Analysis

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PopCapture

Belgium
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Posted - 10/24/2007 : 6:58:48 PM

I need to fit the data points to an exponential equation P = Ae^(bV), where P is pressure (mm Hg), V (mL) is the volume, A and b are constants indicating the position and rate of the curve.

Next I need to determin A and b constants by using the least-square linear regression analysis of the linear form of the equation lnP = lnA + bV.

I would appreicate any value lead as to how to do these step using Origin 7.

Mike Buess

USA
3037 Posts

Posted - 10/27/2007 : 06:14:55 AM

For general instructions on creating a fitting function see Analysis: Curve Fitting> The Nonlinear Least Squares Fitter> User-Defined Fitting Functions in the Origin 7 or 7.5 reference (Help> Origin). If you have an earlier version of Origin then this article might be useful...
http://www.originlab.com/index.aspx?s=9&pid=537

Your fitting functions will be y = A*exp(b*x) and y = ln(A) + b*x. Columns V(X) and P(Y) will be the independent (x) and dependent (y) variables for the first function. You'll need to create another column, lnP(Y), and Set [its] Column Values to ln(col(P)) to get the dependent variable for the second function.

Mike Buess
Origin WebRing Member

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