non linear curve fitting from lvm file

[atoz]

Hi,

I am currently trying to get the fitting equation from a set of data (x and y) in lvm file. I am using the curve fitting vi under mathematics > fitting.

I am using the nonlinear fitting function of this vi and the equation is as follow:

y = a-0.15*2-b/x-c*x+d*ln(x)+e*ln(1-x)

however whenever i try to run the program, it shows an error pointing to the curve fitting vi stating this:

Analysis:  Input parameters has at least one element that is Inf, NaN, DBL_MAX, or DBL_MIN

what could be the problem?

Regards,

atoz

[altenbach]

Hard to tell from the information given.

Can you attach your VI?

Is one of the x values zero? You have a division by x, so that would result into a NaN.

Do you use reasonable guesses for the 5 parameters?

[atoz]

Thanks for the quick response. This attachment are the vi and the lvm file from measurement i have. I do not have a point which is exactly zero. I am not too sure about the initial guess as well.

Regards,

atoz

[altenbach]

• Well, the last value is x=0, so 1/x will fail.
• A lot of points at the beginning are x>1, so ln(1-x) will be undefined too.

I haven't looked in detail at your function, but it seems insufficient to describe the data. Can you point me to a website describing the model in more detail?

[atoz]

Thanks for the reply.

Actually the function is taken from a research paper on a Kalman Filter for battery state-of-charge estimation. it is describing the battery terminal voltage interm of the state-of-charge.

Regards,

atoz

[altenbach]

Do you have a link to the research paper?