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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 ?

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)

Show 3 older comments

Image Analyst on 2 Jun 2013

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

the cyclist on 2 Jun 2013

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

the cyclist on 2 Jun 2013

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:

clc; % 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);

the cyclist on 2 Jun 2013

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

## 1 Comment

Direct link to this comment:http://www.mathworks.com/matlabcentral/answers/77739#comment_152432

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