MATLAB: Curve fitting with constraints

curve fittingCurve Fitting ToolboxexponentialMATLAB

Hi,

I am trying to fit an curve with an exponential function and need it to pass through (0,0) with a gradient of 0 at that point.

I've attached a picture of the data and curve. I am trying to use to the curve fitting toolbox to do this.

Any ideas would be greatly appreciated

Thanks

Best Answer

Using the 'power1' fit type, I obtain pretty close agreement.


>> cfit = fit(x1(x1>0),y1(x1>0),'power1')
cfit = 
     General model Power1:
     cfit(x) = a*x^b
     Coefficients (with 95% confidence bounds):
       a =    -0.07755  (-0.07888, -0.07622)
       b =       3.316  (3.312, 3.32)
       
>> plot(cfit,x1,y1)

Related Solutions

MATLAB: Set sum of coefficients to equal 1 in biexponential fit

You are using the exp2 model form

ft = fittype('exp2')
ft = 
     General model Exp2:
     ft(a,b,c,d,x) = a*exp(b*x) + c*exp(d*x)

except that you wish to have the addirional constraint that a+c == 1.

Trivial. Just build the constraint into the model.

ft = fittype('a*exp(b*x) + (1-a)*exp(d*x)','indep','x')
ft = 
     General model:
     ft(a,b,d,x) = a*exp(b*x) + (1-a)*exp(d*x)

MATLAB: How to get the information from the fitting result

f.a
f.b
confint(f)

Best Answer

Related Solutions

MATLAB: Set sum of coefficients to equal 1 in biexponential fit

MATLAB: How to get the information from the fitting result

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