MATLAB: Column into row

convertmatrixrow

hi just a simple question here, so i got this code:

X=linspace(1,10,10);
Y=linspace(1,10,10);
[xx,yy]=meshgrid(X,Y);

as a result x and y 10 by 10 matrix. how should i do if i want to convert xx and yy to 100 by 1 matrix,so for example second row of xx occupied 1st row 11th to 20th column of xx, 3rd row occupied 1st row 21th to 30 th column, etc

thanks for the help! appreciate much!

Best Answer

doc reshape()

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D = reshape(cat(1, C{:}), 10, [])

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Rob,

I think the problem is that on the last line of your code, i.e.,

ff=10*xx^0.5-3*yy^1.2 +2*yy;

you're taking the matrix square root of xx and not of each matrix element individually. What you probably want to do is the following:

ff=10*xx.^0.5-3*yy.^1.2 +2*yy;

( Notice the point in xx.^0.5. This is an elementwise operation, it basically will take the square root of each individual element, rather than from the entire matrix).

I wrote a little example to explain the difference between elementwise and full matrix operations:

% generate random matrix
A = rand(2,2)
% calculate 2th power of A
A^2
% observe that the same result is produced by A*A
A*A
% observe that the result is different from A.^2
A.^2
% when taking the (1/2)th power (= square root), complex numbers arise
B = A^0.5
% observe that B*B = A
B*B

The warning you get, relates to the matrix xx, which is close to singular. Remember that a matrix is singular iff it has a zero eigenvalue. The fact that xx is close to singular can be observed by having a look at its eigen values:

lambda = eig(xx);
disp(sprintf('The last and smallest eigenvalue is %d', lambda(end)))

You can observe the last (and smallest) eigenvalue is 1.6421e-142. This last eigenvalue is so small, that it renders the square root calculation of xx inaccurate.

Best Answer

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