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I encountered with Ax=0, A is complex matrix, it used [U,S,V]=svd(A,0) and x=V(:,end) which makes sense.

However, it continues D=diag(abs(x)), [Q,R]=qr((AD).'), x=DQ(:,end);

What's these last operations for (all in Matlab code)?

Thank for help.

Apple
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    You might get more help if you translate your question from code into mathematics. If you’re just trying to find a single element of the kernel of $A$, extracting a right singular vector with singular value 0 sounds reasonable. – user7530 Jan 01 '18 at 00:43
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    You should advise your Readers where you encountered this Matlab code and what mathematical task you are attempting. – hardmath Jan 01 '18 at 00:44
  • I think that it is qr((A*D).') with a multiplication sign. Moreover DQ(:,end) has no meaning as long as you don't define DQ ... – Jean Marie Jan 01 '18 at 01:06
  • In order to answer the question in your title, qr is the important operation of decomposition of a matrix into a product Q*R of an orthogonal matrix by an upper triangular matrix. Why they use it here is another question. – Jean Marie Jan 01 '18 at 01:08
  • Hi, Jean: The AD and DQ should be A * D and D * Q. The question is a math question that I don't understand the operation of doing more on x after it's solved by V(:,end). I need to know why in order to translate it o Mathematics. – Apple Jan 02 '18 at 15:43
  • qr is the orthogonal-triangular decomposition, Q(:,end) is the right most column of the Q matrix. – Apple Jan 02 '18 at 15:52

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