matrix error in wave fitting?

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 singular matrix or other numeric error.

I don't understand the error and it should not show this when fitting a curve or am I missing something?

Function Rishabhsircronicles(w,x) : FitFunc
    Wave w
    Variable x
    variable    k,ka,k1,k2
    k=(7.64*(10^-(12))) //ka =0.00000000000764
    ka=225
    variable p,q
    p=((k/2)*(ka/x))
    q=((k/3)*(ka/x))
    
    //CurveFitDialog/ These comments were created by the Curve Fitting dialog. Altering them will
    //CurveFitDialog/ make the function less convenient to work with in the Curve Fitting dialog.
    //CurveFitDialog/ Equation:
    //CurveFitDialog/ f(x) = f(x) = w+a*((2/exp(h/(2*kb))*(w/T))+1)+b*(1+(2/((exp(h/(3*kb))*(w/T))-1))+(3/(exp((h/(3*kb))*(w/T))-1)^2)
    //CurveFitDialog/ End of Equation
    //CurveFitDialog/ Independent Variables 1
    //CurveFitDialog/ x
    //CurveFitDialog/ Coefficients 2
    //CurveFitDialog/ w[0] = a
    //CurveFitDialog/ w[1] = b
    k1=(w[0]*(  (   2/(exp(p)   -1) )   +1  )   )
    k2= (w[1]*( 1+  (   2/( exp(    q)-1    )   )   +   (   3/((exp(q) - 1  )^2)  ) )   )
    
    return ka+K1+K2
    
End


 

 curvefitting dialog wave selected error shown by curve fitting dialog trace information dialog Equation that I wrote in the procedure

k=(7.64*(10^-(12))) //ka =0.00000000000764

My guess is a numerical problem, probably a zero derivative caused by floating point underflow, or by small differences of large numbers. Possible solutions might be:

1. Use an Epsilon wave: DisplayHelpTopic "The Epsilon Wave"

2. Rescale your problem to avoid extreme values.

September 10, 2018 at 09:15 am - Permalink

Re-cast your equations so that k is close to 1. There may be other problems as well.

September 11, 2018 at 03:35 pm - Permalink