# continuity of a fit function in different regions

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Answered: Alex Sha on 23 Feb 2020 I have probelm in continuity of a fitting of a function where I divided it to two regions the first region is linear and second one is quadratic where I'm using lsqcurvefit for fitting

Alex Sha on 23 May 2019

you can find the data in the attchment and I want to have the derivative of the function at x=1 to be zero.
thank you

Alex Sha on 23 Feb 2020
Hi, the function below meets your requirements， with the derivative to be zero at x=1
y = p1+p2*(((x-p3)*(x+p4))^2)^p5;
Root of Mean Square Error (RMSE): 0.111454525338652
Sum of Squared Residual: 0.236020113150822
Correlation Coef. (R): 0.999608307854672
R-Square: 0.999216769132081
Determination Coef. (DC): 0.999216769132081
Chi-Square: 0.322625091206584
F-Statistic: 4465.16963433769
Constrained Functions: p2*((p5*((((1-p3)*(1+p4))^2)^(p5-1)))*((2*((1-p3)*(1+p4)))*(1+p4+1-p3)))-0 = 0
Parameter Best Estimate
---------- -------------
p1 12.2679122419038
p2 -12.1133796289348
p3 1.00000000000003
p4 -0.999999999999971
p5 0.321345944716431 