Multiplication of elements in array

Hi everyone, I have b=[1 1 1; 1 2 4; 1 3 9; 1 4 16] and k=1:5, I want to have 4 different set of numbers.

There are total 4 rows in set b.

To form the first set of number which denoted as kb1, I take the numbers from first row from set b, which is [1 1 1].

For the first row of kbl=k(1)*[1 1 1]

For the second row of kb1=k(2)*[1 1 1]

For the third row of kbl=k(3)*[1 1 1]

For the fourth row of kb1=k(4)*[1 1 1]

And finally for the fifth row of kbl=k(5)*[1 1 1].

Next follow by second set of the numbers,which denoted as kb2=k*[1 2 4]

So at the last I will have 4 set of numbers,

How can i do this?

Thanks

Answer 1

[Cedric]

And if you aren't too familiar with Andrei's singleton expansion in 3D numeric arrays ;-), here is a simpler and less compact solution, which creates a cell array of results..

 nRows = size( b, 1 ) ;

 % Initialize (prealloc) cell array of results.
 kbs = cell( nRows, 1 ) ;

 % Loop over rows of b and build kdbs.
 for rId = 1 : nRows
     kbs{rId} = bsxfun( @times, k(:), b(rId,:) ) ;
 end

Then, to get e.g. what you would name kb3, you index teh content of cell #3 of the cell array kbs:

 >> kbs{3}
 ans =
     1     3     9
     2     6    18
     3     9    27
     4    12    36
     5    15    45

Note that in the clal to BSFUN, k(:) is a k developed as a column vector, and b(rId,:) is a row vector of elements of row rId of b:

 >> k(:)
 ans =
     1
     2
     3
     4
     5

 >> b(3,:)          % Row 3 for example.
 ans =
     1     3     9

Then what BSXFUN does roughly is to repeat both vectors as many times as there are rows/columns in the other vector (along the non-singleton dimension) to generate (internally) the following arrays:

     1   1   1                1   3   9
     2   2   2                1   3   9 
     3   3   3                1   3   9
     4   4   4                1   3   9
     5   5   5                1   3   9

These arrays are then multiplied element by element, as you passed @times - a handle on the element-wise multiplication - as the first argument in the call to BSXFUN.

Answer 2

[Andrei Bobrov]

kb = bsxfun(@times,permute(b,[3,2,1]),k(:));

add

kb = num2cell(bsxfun(@times,permute(b,[3,2,1]),k(:)),[1 2]);
kb_cell = kb(:);

[Grace]

Hi Andreo,

Sorry, this is not what I want to get.

The following are the one that I wish to get:

For kb1=[1 1 1;1 1 1; 1 1 1; 1 1 1;1 1 1]

For kb2=[1 2 4; 1 4 8; 3 6 12; 4 8 16; 5 10 20]

For kb3=[1 3 9; 2 6 18; 3 9 27; 4 12 36; 5 15 45]

For kb4=[1 4 16; 2 8 32; 3 12 48; 4 16 64; 5 20 80]

Thanks.

[Andrei Bobrov]

corrected