a and b constant

Question

MOHAMED YHYA 2019-4-21

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https://ww2.mathworks.cn/matlabcentral/answers/457656-a-and-b-constant

回答： Image Analyst 2019-4-21

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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Answer 1

Image Analyst 2019-4-21

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在 MATLAB Online 中打开

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 2

Stephan 2019-4-21

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编辑：Stephan 2019-4-21

在 MATLAB Online 中打开

% 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);