# How can I create a matrix with the values of the elements is a function of the indices?

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Benjamin Schuessler
on 6 Jan 2018

Commented: Cedric Wannaz
on 6 Jan 2018

I am trying to create a matrix from two vectors (i.e. A = [0:2] and B = [-2:2]) where the values for each cell of the matrix is a function of the indices. I cannot see the path to get it there, any simple examples I can follow?

Thanks

##### 3 Comments

### Accepted Answer

Cedric Wannaz
on 6 Jan 2018

Edited: Cedric Wannaz
on 6 Jan 2018

Not sure that I understand. If you wanted to create a rectangular array whose elements are a the result of some arithmetic operation between corresponding elements of A and B, you could use the fact that MATLAB expands automatically operands of such operations (from 2016b on, otherwise you have to use BSXFUN):

>> A = 0 : 2 ; B = -2 : 2 ;

>> A.' .* B

ans =

0 0 0 0 0

-2 -1 0 1 2

-4 -2 0 2 4

Note that here we first make A a 3x1 column vector by transposition. Then we apply an element-wise operation ( .* ) between this transpose and B that is 1x5, and MATLAB expands automatically A.' along B and vice versa (hence building 3x5 arrays) and performs the operation.

If you needed to apply a function that is not an arithmetic operation, you could do it using BSXFUN (performing an explicit call to a function that does an implicit expansion..):

>> result = bsxfun( @plus, A.', B )

result =

-2 -1 0 1 2

-1 0 1 2 3

0 1 2 3 4

or through an explicit expansion (using REPMAT, REPELEM, or MESHGRID):

>> [Bx, Ax] = meshgrid( B, A )

Bx =

-2 -1 0 1 2

-2 -1 0 1 2

-2 -1 0 1 2

Ax =

0 0 0 0 0

1 1 1 1 1

2 2 2 2 2

applying whatever function to the two arrays:

>> plus( Ax, Bx )

ans =

-2 -1 0 1 2

-1 0 1 2 3

0 1 2 3 4

##### 2 Comments

Cedric Wannaz
on 6 Jan 2018

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