Fitting a quadratic model with the coefficient of linear term fixed

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?

Answer 1

[Ameer Hamza]

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);