how can I change in a Matrix 4x7 a certain numbers in the Matrix from positive to negative or vise versa by using ind2sub function.

how can I change in a Matrix 4x7 a certain numbers in the Matrix from positive to negative or vise versa by using ind2sub function.

For example:

1 2 3 5 4 5 6

3 9 3 0 29 9 8

57 64 2 5 8 1 9

3 8 3 2 4 7 10

To the negative value when the numbers are less than 10 and vice versa.

Answer 1

[Ameer Hamza]

No need to use ind2sub. Just use logical indexing

A(A<10) = -A(A<10);

Another method

idx = find(A < 10);
A(idx) = -A(idx);

And finally: if you really want to use ind2sub()

idx = find(A < 10);
[r, c] = ind2sub(size(A), idx);
for i = 1:numel(r)
    A(r(i), c(i)) = -A(r(i), c(i));
end

[GreyHunter]

Thanks very much for your reply,

I was trying to do something like this:

A(ind2sub([4,7],find(R<10)))= -find(R<10).

[GreyHunter]

But it seems it changes also the numbers.

[Ameer Hamza]

This is the correct syntax if you want to do it like that.

A(ind2sub([4,7],find(A<10))) = -A(find(A<10));

However, it is an inefficient approach; MATLAB will also give a warning.