Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Curve fitting to diffusion equation(Matlab)

  1. Nov 25, 2010 #1
    We have been trying to fit experimental diffusion results to the diffusion equation using Matlab to evaluate the Diffusion coefficient.
    The equation we used:
    Experimental values [x],[y] and t are given. C and D are to be evaluated from the curve fit.
    We used cftool of Matlab.
    We have a problem in getting the results. We get error message as:

    "Error using ==> <a href="error:C:\Program Files\MATLAB\R2007b\toolbox\curvefit\curvefit\@fittype\feval.m,97,0">fittype.feval at 97</a>
    Error in fittype expression ==> C.*erfc(x./(2.*sqrt(D.*300)))
    ??? Error using ==> erfcore
    Input must be real."

    Can anyone help?
  2. jcsd
  3. Nov 25, 2010 #2
    It looks like the problem is that the error function requires real input arguments. Looking at your expression I would say the most likely problem is that the D parameter gets negative during the fitting, and as such maybe you could try to use abs(D) instead, although this could lead to the fitting algorithm having problems finding the right values.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Curve fitting to diffusion equation(Matlab)
  1. Curve fitting (Replies: 0)