fitted curve start from zero?

How can the fitting curve can stat from [0,0]?

Answer 1

[Star Strider]

The easiest way is to not specify a y-intercept in the model you want to fit.

Example —

x = 0:2:100;
y = 3E+3 - (x-50).^2 + (x-50) + randn(1, numel(x))*50;

B = [x(:).^2 x(:)] \ y(:);
Y = [x(:).^2 x(:)] * B;

figure
plot(x, y, '.',    x, Y, '-r')
grid

Here, x begins at 0, and not including a y-intercept in the model is the same as forcing it through 0.

Experiment to get the result you want, with your model and data.

[Davide Cerra]

thank you,

is thera an easy way to impose constraints in the curve fitting toolbox?

[Star Strider]

My pleasure.

You can impose some constraints with lsqcurvefit and the other Optimization Toolbox functions. This depends on what you want to constrain.

I don’t have the Curve Fitting Toolbox. (I can do everything I need with the Optimization and Statistics and Machine Learning Toolboxes.)