MATLAB: Curve fitting options give two diffrent results

curvefitting

I am getting two different solutions and goodness of fitting on using same equation and fitting options in Curve fitting tool.
I am using two terms exponential fitting as a*exp(b*x)+c*exp(d*x) with nonlinear LeastSquare , LAR and Trust region algorithm. I am getting goodness of fit : SSE=902.8; RMSE= 1.456
Same equation if I use in custom equation with similar fit options, neither I get similar coefficient values nor similar goodness of fit:
SSE= 8.55 e+14 RMSE= 1.417e+06
Please let me know why it so??

Best Answer

Your results will be sensitive to starting point. As long as you use the same equation and a close enough starting point you must get similar results.
Click on Fit Options and see what the bounds and starting point is for the exponential fitting, and use the same for your custom equation.
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