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Fitting two data sets

msc05msc05 Posts: 2Member
I have too sets of data. I want to fit with the expressions

y=a*log(x/b) and y=c*log(x/b)

Is there any way to fit both expressions simultaneously to obtain b?

thanks in advance
msc05

Comments

  • jjasso5jjasso5 Posts: 41Member
    Yes, it's possible but not trivial.

    You may use optimization techniques (at least).
    If you know a and c, then you may use use fminbnd to
    find b.

    If you want to find a, b and c, then you may use
    fminsearch, or other functions within the
    Optimization Toolbox. I like fminbnd and fminsearch
    because they're standard functions.

    You have to define an "objective function". You have
    to prepare it in such a way, that its minimum value
    becomes your solution. Its minimum value is going to
    be found by fminbnd (finds only one variable) or
    fminsearch (finds more than one variable).

    It's possible but not trivial...

    Here are two nice examples of curve fitting:
    http://www.matrixlab-examples.com/nonlinear-programming.html
    http://www.matrixlab-examples.com/exponential-regression.html

  • msc05msc05 Posts: 2Member
    I think I have found another way out of the problem. My plan is to translat one of the data sets along the x-axis and then fit by the expression

    y=a*log(x/b) for x=[0;1000], y=c*log(x/b) for x=[1000;inf]

    How do I write such an expression in Matlab?
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