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a and b constant

Asked by MOHAMED YHYA on 21 Apr 2019
Latest activity Answered by Image Analyst
on 21 Apr 2019
HI, im new to matlab and was wondering how would you input a command to help me solve an unknown constant in an equation.
I have a bunch of x,y points,The equation would be x= a*y+b

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2 Answers

Answer by Image Analyst
on 21 Apr 2019
 Accepted Answer

You say "The equation would be x= a*y+b" and this is the opposite to the way people usually do things, but it can be done. Just reverse x and y when you call polyfit(). Try this:
coefficients = polyfit(y, x, 1); % x as a function of y - note NOT the usual way people do things!
a = coefficients(1)
b = coefficients(2)

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Answer by Stephan
on 21 Apr 2019
Edited by Stephan
on 21 Apr 2019

% Only needed if x,y are not column vectors
x = reshape(x,[],1);
y = reshape(y,[],1);
% solve for a, b
x = [x, ones(numel(x),1)];
sol = y\x;
a = sol(1);
b = sol(2);

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