MATLAB Answers


regress(x,y) for least square regression of two variables x,y

Asked by mohamed
on 2 Jun 2013

when i use regress(x,y),I obtain only one answer :shouldn't i get two answers which are the slope and y-intercept ?

  1 Comment

my code is x=[1 4 5 6];y=[4 6 7 9]

2 Answers

Answer by the cyclist
on 2 Jun 2013
 Accepted answer

You don't show us your code, but I am guessing you neglected to add a column of ones to your x input, as described in the documentation:

doc regress

This code will give you the two-parameter output you expect:

x = [ones(3,1),rand(3,1)];
y = rand(3,1);
b = regress(y,x)


But I did answer that here. Did you ever look at where you first asked it?

@Image Analyst, I answered there, too, and did not realize it was the same poster! sigh

b = regress(z',[ones(4,1) x' y']);

combines x and y into one array, adds the column of ones that you need, and then does the regression with z.

Answer by Image Analyst
on 2 Jun 2013

I don't have regress(). Please list what Product (toolbox) is is in below your question in the Product box.

You can use polyfit() which is in base MATLAB to get the slope and intercept in one line. Here's a full blown demo:

% Create training data:
x = [1 4 5 6]
y = [4 6 7 9]
% Do the regression.
coefficients = polyfit(x, y, 1); % 1 means a line
slope = coefficients(1)
intercept = coefficients(2)
% We're done!
% Plot training data:
plot(x, y, 'bo', 'LineWidth', 3);
hold on;
% Plot fit
numberOfPoints = 100;
fitX = linspace(min(x), max(x), numberOfPoints);
fitY = polyval(coefficients, fitX);
plot(fitX, fitY, 'r-', 'LineWidth', 3);
grid on;
xlabel('X', 'FontSize', 30);
ylabel('Y', 'FontSize', 30);

  1 Comment

I always forget that regress() is not in core MATLAB. I added the Statistics Toolbox product tag.

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