Fitting a quadratic model with the coefficient of linear term fixed

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Anand P
Anand P 2020-3-19
回答： Ameer Hamza 2020-3-19
A quadratic equation is given by y = ax^2 + b^x +c.
Matlab function 'fit' is used to fit a relation between input and output.
I need to fit a quadratic function between input and output with the coefficient b fixed. How is that done in MATLAB?

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Ameer Hamza
Ameer Hamza 2020-3-19
You can use fittype to specify the type of function you want to fit
x = linspace(0, 2, 100);
y = 2*x.^2 + 3*x + 4;
ft1 = fittype('a*x^2+b*x+c');
fit1 = fit(x',y',ft1);
ft2 = fittype('a*x^2+2.5*x+c'); % <--- fix the coefficient of x
fit2 = fit(x',y',ft2);

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