How to subtract only certain elements of a vector

Question

Stacy Genovese 2022-5-5

回答： John D'Errico 2022-5-5

If I have two vectors of the same length, is it possible to subtract only certain elements?

a = [1 4 6 7; 3 4 5 6]
b = [4 2 7 8; 2 6 7 8]

normally I would do:

a(1,:) - b(1,:)

But how do I the same subtraction but only with elements 1,2 and 4?

Is this possible to do? Which element I want to skip will change each time through my loop.

Thanks

Answer 1

John D'Errico 2022-5-5

a and b are not vectors in your question, they are arrays.

However, if you want to do this, nothing stops you from selecting the elements you wish to subtract, and do so.

a = [1 4 6 7; 3 4 5 6];
b = [4 2 7 8; 2 6 7 8];
ind = [1 2 4];
c = a(1,ind) - b(1,ind);
c
c = 1×3
    -3     2    -1