Assignment of values in an empty matrix by logical indices

I have the following behavior but I expected another one:

>> H=zeros(3,0)

H =

   Empty matrix: 3-by-0

>> H(3,false)=1

H =

   Empty matrix: 3-by-0

>> H(4,false)=1

H =

   Empty matrix: 4-by-0

It seems the value is not assigned but the matrix dimension is extended. Maybe someone is able to explain this behavior.

Thanks Stefan

Answer 1

[David Sanchez]

matlab start indexing arrays with 1. Arrays in Matlab do not have element in position 0.

H(3,false) = H(3,0)

what does not exist: you do not change anything with that line.

H(4,false) add an extra row to the original matrix but does not assign a value to its elements since H(4,0) is not an element.

Answer 2

[Jos (10584)]

For a matrix M, and scalars R, C and V, the expression

M(r,c) = V

means that you want to set the value of the Rth row and Cth column of the matrix M to the value V. If that row or column does not exist, create it.

For a logical vector TF

M(r,TF) = V

means to set the elements of the Rth row and the columns where TF is true to the value V. Again, if row R does not exist, create it.

So, the following makes sense:

A = 2,  A(2,3) = 4 
B = zeros(2,0), B(3,[false true false]) = 99

Answer 3

[Stefan]

Thanks for fast reply. I still wondering that it is possible to assign values to a non existent element of matrix. However, I understand the issue and can handle it.

Regards Stefan