How do i create two multi-dimensional arrays:  a 10 x 10 x 10 numerical array (3-D) anda 5 x 5 x 5 x 5 numerical array (4-D) where each value in each array corresponds to the multiplication of indices?

Pls advice

Answer 1

[Nobel Mondal]

This could be another approach:

A = ones(10, 10, 10);
for i=1:10
  A(i,:,:) = A(i,:,:)*i;
  A(:,i,:) = A(:,i,:)*i;
  A(:,:,i) = A(:,:,i)*i;
end

Answer 2

[Walter Roberson]

Hint:

[A,B] = ndgrid(1:3, 1:7);
Q = A .* B;

Answer 3

[Stephen23]

This can be done quite simply using matrix multiplication and a single bsxfun call:

3D

>> X = 1:10;
>> Y = X(:)*X;
>> bsxfun(@times,Y,reshape(X,1,1,10))
ans(:,:,1) =
   1     2     3     4     5     6     7     8     9    10
   2     4     6     8    10    12    14    16    18    20
   3     6     9    12    15    18    21    24    27    30
   4     8    12    16    20    24    28    32    36    40
   5    10    15    20    25    30    35    40    45    50
   6    12    18    24    30    36    42    48    54    60
   7    14    21    28    35    42    49    56    63    70
   8    16    24    32    40    48    56    64    72    80
   9    18    27    36    45    54    63    72    81    90
  10    20    30    40    50    60    70    80    90   100
...
ans(:,:,10) =
  10    20    30    40    50    60    70    80    90   100
  20    40    60    80   100   120   140   160   180   200
  30    60    90   120   150   180   210   240   270   300
  40    80   120   160   200   240   280   320   360   400
  50   100   150   200   250   300   350   400   450   500
  60   120   180   240   300   360   420   480   540   600
  70   140   210   280   350   420   490   560   630   700
  80   160   240   320   400   480   560   640   720   800
  90   180   270   360   450   540   630   720   810   900
 100   200   300   400   500   600   700   800   900  1000

4D

>> X = 1:5;
>> Y = X(:)*X;
>> bsxfun(@times,Y,reshape(Y,1,1,5,5))
ans(:,:,1,1) =
   1     2     3     4     5
   2     4     6     8    10
   3     6     9    12    15
   4     8    12    16    20
   5    10    15    20    25
...
ans(:,:,5,5) =
  25    50    75   100   125
  50   100   150   200   250
  75   150   225   300   375
 100   200   300   400   500
 125   250   375   500   625

Answer 4

[Mohmmadsoaib Diwan]

array_3D=zeros(10,10,10);

if true
  % code
endfor x=(1:10)
  for y=(1:10);
      for z=(1:10);
          array_3D(x,y,z)=(x*y*z);
      end
  end
end
array_4D=zeros(5,5,5,5);
for x=(1:5)
  for y=(1:5)
      for z=(1:5)
          for t=(1:5)
              array_4D(x,y,z,t)=(x*y*z*t);
          end
      end
  end
end

Answer 5

[Charlie Elverson]

I think something like this would work:

my_array = zeros(10, 10, 10)
for i = 1:10
for j = 1:10
for k = 1:10
my_array(i,j,k) = i*j*k;
end
end
end

This could obviously be made more general, but you get the idea. The 4-dimensional case is a simple extension of the above.

[Yeap Jia Wei]

how about the multiplication of indices ?

[Nobel Mondal]

What about this line?

my_array(i,j,k) = i*j*k;

Answer 6

[Andrei Bobrov]

variant

3D:

n = [10 10 10];
A = bsxfun(@times,(1:n(1))'*(1:n(2)),reshape(1:n(3),1,1,[]));

4D:

n = [5 5 5 5];
A = bsxfun(@times(bsxfun(@times,(1:n(1))'*(1:n(2)),...
                           reshape(1:n(3),1,1,[])),reshape(1:n(4),1,1,1,[]));

other variant:

n=[4 5 2 3];
nn = numel(n);
z = cell(nn,1);
ii = arrayfun(@(x)1:x,n,'un',0);
[z{:}] = ndgrid(ii{:});
out = prod(cat(nn+1,z{:}),nn+1);