how to reshape an n x 1 matrix into a squre matrix using matlab?

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ramesh jallu 2011-3-3

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hi experts........... greetings to all. hear a challenge question? how to reshape an n x 1 matrix into a square matrix using matlab?please let me know.i would be grateful to you.i am waiting for solution.

thanks in advance

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Answer 1

Jos (10584) 2011-3-4

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This function will take any vector (or even a matrix) V and reshapesit into the smallest square matrix that can hold it. Note that it does not use reshape.

function M = reshapeVintosquareM (V)
% Reshapes a vector into the smallers square matrix possible. If V is too short
% the remainder of M is filled with NaNs.
N = numel(V) ;
M = NaN(ceil(sqrt(N))) ;
M(1:N) = V ;

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Walter Roberson 2011-3-4

Yep, there are special-cases of my code for some specific fill values such as nan:

SQ = nan(ceil(sqrt(length(vec)))); SQ(1:length(vec)) = vec;

ramesh jallu 2011-3-5

thanks my friend

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Answer 2

Andreas Goser 2011-3-3

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The answer is already in your question. RESHAPE.

x=[1 2 3 4 5 6 7 8 9];
reshape(x,3,3)

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Walter Roberson 2011-3-5

Sorry, Matlab is not able to handle that situation because Matlab uses finite precision arithmetic, and the situation you outline requires infinite precision arithmetic in order to properly be able to distinguish between indices 4.1231056256176605498214098559740770251471992253736, sqrt(17), and 4.1231056256176605498214098559740770251471992253737

ramesh jallu 2011-3-5

thanks for your awesome response

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Answer 3

Walter Roberson 2011-3-4

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Vectors which are not the square of a positive integer can be accomodated, if the unused spaces can be filled with some specific value of the same data class as the array values.

SQ = FillValue * ones(ceil(sqrt(length(vec)))); SQ(1:length(vec)) = vec;

The above will also work for vectors which would form perfect squares.

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Jan 2011-3-4

What an excellent service. You get ultimative solutions even for very basic questions.

I hope that Ramesh is goind to accept an answer.

ramesh jallu 2011-3-5

thanks dude

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Answer 4

David Young 2011-3-3

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The SQRT function may be useful here.

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ramesh jallu 2011-3-5

can we do that by adding some dummy rows and columns?

Walter Roberson 2011-3-5

Adding dummy rows or columns would be contrary to the requirement that "after reshaping product of dimensions should be same".

If n is composite, it would be possible to arrange n in to a rectangle and add dummy rows and columns such the the result was a square matrix. If n is prime, then you would have to add (n-1) dummy rows (or columns) of length n in order to form a square.

I would have to think a bit to come up with an algorithm for determining the fewest total dummy rows and columns necessary to create the square matrix. I suspect that might also be the same solution as "the lowest total number of dummy elements added" but I am too tired at the moment to prove it mentally.

In the above discussion, I am assuming that n must be arranged in to a rectangle. The answer I gave above with SQ is based upon arranging n in to a square that has just a single partial strip of elements missing and filling those missing elements with a dummy value.

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Answer 5

Paulo Silva 2011-3-4

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function [SQmatrix,flag]=vec2SQmat(vec)
%[SQmatrix,flag]=vec2SQmat(matrix)
%
%This function receives a vector and tries
%to convert it to a square matrix SQmatrix
%flag indicates the sucess (1) or failure (0)
%
flag=0; 
sq=sqrt(numel(vec));
if (round(sq)==sq)
SQmatrix=reshape(vec,sq,sq);
flag=1;
end