MATLAB: Differentiation of two variables in a polynomial equation

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Please the differential part gives giving me empty curly brackets instead of values in this code set.
% Initial x1 and x2
x1 = 5, x2 = 4
% Equations
y1 = (x1-3)^2 + (2*x2 - 8)^2
y2 =(x1-4)^2 + (x2 - 10)^2
%Given y values
y = [5;49]
% First set of y values
yo = [y1;y2]
f = y - yo
A11 = diff(poly((x1-3)^2 + (2*x2 - 8)^2),x1)
A12 =diff(poly((x1-3)^2 + (2*x2 - 8)^2),x2)
A21 =diff(poly((x1-4)^2 + (x2 - 10)^2),x1)
A22 =diff(poly((x1-4)^2 + (x2 - 10)^2),x2)
| I was expecting to see this: | http://www.mathworks.com/matlabcentral/answers/uploaded_files/25540/Capture.JPG
or http://www.mathworks.com/matlabcentral/answers/uploaded_files/25542/Capture1.JPG
Thank you.

Best Answer

x1 and x2 are numbers. You set them as such. Remember this line?
x1 = 5, x2 = 4
you cannot differentiate with respect to a number.
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