what does c(:).' mean? c should be a vector

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Hi I saw this in Matlab document:
function obj = DocPolynom(c)
% Construct a DocPolynom object using the coefficients supplied
if isa(c,'DocPolynom')
obj.coef = c.coef;
else
obj.coef = c(:).';
end
end
What does c(:).' mean? Is .' the transpose of each element? But I think c should be a vector here. Any help's appreciated. Thanks!

Accepted Answer

Matz Johansson Bergström
Matz Johansson Bergström on 24 Aug 2014
By writing c(:)' you are making sure that the vector has the dimension 1xn, where n is the length of the vector, a row vector. However, there is a very important difference between c(:).' and c(:)', because they are not the same.
The difference is when you are working with complex vectors, for instance
tmp = (1:5) + 1i;
tmp(:).'
which gives you each complex number in a row vector, compared to
tmp(:)'
which is giving you a row vector of the complex conjugate of each element.

More Answers (1)

Roger Stafford
Roger Stafford on 24 Aug 2014
This is a short way to reshape c, whether it is a vector or array, into a row vector. You are then guaranteed that obj.coef will be a vector with just one row and however many columns as there are elements in c.
reshape(c,[],1)
will do the same thing.
  4 Comments
Roger Stafford
Roger Stafford on 24 Aug 2014
No, the dot prevents matlab from taking the complex conjugate of elements along with the transposition. It has nothing to do with element-by-element operation. Their documentation says: "b = a.' computes the non-conjugate transpose of matrix a and returns the result in b" and "b = a' computes the complex conjugate transpose of matrix a and returns the result in b."
If c is entirely real-valued, then c(:).' and c(:)' are the same.
Yuji Zhang
Yuji Zhang on 25 Aug 2014
Ahh I see that! So the dot has two meanings! Thanks a lot for your help Roger!

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