MATLAB: How to perform a linear least squares fit

MATLAB

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

Best Answer

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

Related Solutions

MATLAB: Fit and Polyfit (LAR vs. Least squares)

You can find out by asking for the output argument:

[fitobject,gof,output] = fit(x,y,fitType)
output.algorithm

But the real difference between fit and polyfit are the options that you can choose as well as polyfit is strictly limited to polynomials and uses the least squares method.

MATLAB: How to plot best fit line

Use polyfit() and polyval():

% Get coefficients of a line fit through the data.
coefficients = polyfit(x, y, 1);
% Create a new x axis with exactly 1000 points (or whatever you want).
xFit = linspace(min(x), max(x), 1000);
% Get the estimated yFit value for each of those 1000 new x locations.
yFit = polyval(coefficients , xFit);
% Plot everything.
plot(x, y, 'b.', 'MarkerSize', 15); % Plot training data.
hold on; % Set hold on so the next plot does not blow away the one we just drew.
plot(xFit, yFit, 'r-', 'LineWidth', 2); % Plot fitted line.
grid on;

See attached for a full demo.

Best Answer

Related Solutions

MATLAB: Fit and Polyfit (LAR vs. Least squares)

MATLAB: How to plot best fit line

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