reshape, repmat and bsxfun

reshape, repmat and bsxfun.matlab

%% using reshape() to change a multi dimensional array into a smaller 
% dimension without loosing values

%vector into matrix 5x2 (rowxcol)
A = 1:10;
B = reshape(A,[5,2])

%reshape matrix to have 3 columns, discarding rows
A = magic(6);
B = reshape(A,[],3)


%% using repmat() to change a multi dimensional array into a bigger 
A = diag([100 200 300])

%{
A =

   100     0     0
     0   200     0
     0     0   300
%}

B = repmat(A,2) %repeat matrix on 2x2: Create a 2-by-2 tiling of A

%{
B =

   100     0     0   100     0     0
     0   200     0     0   200     0
     0     0   300     0     0   300
   100     0     0   100     0     0
     0   200     0     0   200     0
     0     0   300     0     0   300
%}

%vertical stack of row values
A = 1:4;

B = repmat(A,4,1)
%{
B =

     1     2     3     4
     1     2     3     4
     1     2     3     4
     1     2     3     4
%}

%% 'bsxfun' is much faster
idx = bsxfun(@plus, (0:2)', 1:10)

%{
idx =

     1     2     3     4     5     6     7     8     9    10
     2     3     4     5     6     7     8     9    10    11
     3     4     5     6     7     8     9    10    11    12
%}