How to Vectorize if statement

Dear all,

Here is part of my code for vectorizing the for loop and if statement:

u=zeros(N,1);
du=zeros(n,1);
j=1:1:n 
du(rem(j,5)==1)=u(j+1)-u(N+(j-rem(j,5));
du(rem(j,5)~=1)=u(j+1)-u(N+(j-rem(j,5)-1);

but i got the following error:

In an assignment A(I) = B, the number of elements in B and I must be the same.

Can anyone point out the error for me? Thank you.

Answer 1

[Walter Roberson]

j5 = rem(j,5);
jsel = j5 == 1;
jnsel = ~jsel;

du(jsel)  = u(j(jsel)  + 1) - u(N + j(jsel)  - j5(jsel));
du(jnsel) = u(j(jnsel) + 1) - u(N + j(jnsel) - j5(jnsel) - 1);

Alternately:

j5 = rem(j,5);
jnsel = j5 ~= 1; 

du = u(j + 1) - u(N + j - j5 - jnsel);