How do I perform a linear least squares fit

Hello.

I would like to perform a linear least squares fit to 3 data points.

The help files are very confusing, to the point where i can't figure out whether this is a base function of Matlab, I need the curve fitting toolbox, optimization toolbox, or both.

Thanks,

Alex

Answer 1

[Star Strider]

You don’t need any toolboxes. Use polyfit (link) and polyval functions, or the mldivide (link) operator.

Answer 2

[Image Analyst]

See attached polyfit demo. Adapt as needed. All you need is base MATLAB - no toolboxes.

For example

coefficients = polyfit(x, y, 1);
yFitted = polyval(coefficients, x); % yFitted will be at the 3 points where x is.  There will be 3 yFitted values.

If you want a lot more points, you can pass in more x to polyval():

xFit = linspace(min(x), max(x), 1000); % 1000 points.
yFitted = polyval(coefficients, xFit);

[Alexander MacFarlane IV]

Thanks Star Strider and Image Analyst!

You guys are amazingly fast.

Answer 3

[Tamas Kis]

Function to perform curve fitting using linear least squares:

https://www.mathworks.com/matlabcentral/fileexchange/93710-linear-least-squares-curve-fitting-least_squares_fit

Linear and polynomial fits are linear least square fits, while the other fits (power, exponential, logarithmic) are approximated by first linearizing the data.