I got a code from my professor as an answer to one of our recitation problems and I am trying to decipher it.

The for loop is as follows:

p=1;

q=1;
for i=2:2:2*N                            
    K(i,q:q+2)=[x(p)^2 x(p) 1];          
    L(i)=y(p);                           
    p=p+1;
    K(i+1,q:q+2)=[x(p)^2 x(p) 1];        
    L(i+1)=y(p);                       
    q=q+3;
end

what is the "i=2:2:2*N" part? I thought you only used an i = n:m sort of format. Why are there two colons here? Thank you.

[BN]

2:2:2*n means from 2 to 2*n in the intervals of 2. From:interval:to

Answer 1

[David Hill]

i=2:2:2*N;%advances i by 2 starting at 2 and going until it reaches 2*N

Answer 2

[Steven Lord]

See the Description section on the documentation page for the for keyword. The array over which for iterates can be defined as a:b, but it can also be defined as a:d:b or it can be an arbitrary array over whose columns for should iterate.