# How to vectorize matrix assignment process below

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jyp on 25 Nov 2020
Commented: jyp on 25 Nov 2020
I try to vectorized the following code in the following way to speed up the process. But it doesn't work.
I try to use this code to assign some part of the matrix by values as some functions of the index i (a(i), b(i), .etc).
N=100;
A=zeros(2*N,2*N);
for i=2:N-1
A(2*i-1,2*i-1)=a(i);
A(2*i-1,2*i)=b(i);
A(2*i-1,2*i+1)=c(i);
A(2*i,2*i-3)=d(i);
A(2*i,2*i-1)=e(i);
A(2*i,2*i)=f(i);
end
_______________
vectorized code:
N=100;
A=zeros(2*N,2*N);
i=2:N-1;
A(2*i-1,2*i-1)=a(i);
A(2*i-1,2*i)=b(i);
A(2*i-1,2*i+1)=c(i);
A(2*i,2*i-3)=d(i);
A(2*i,2*i-1)=e(i);
A(2*i,2*i)=f(i);
But matlab says the assignment can be carried out because the dimensions doesn't match. So is there any proper way to do this？

Stephan on 25 Nov 2020
All values from a(i) are overrided by e(i). Same for b(i) and f(i).
jyp on 25 Nov 2020
Sorry for the typos. I've corrected them.

KSSV on 25 Nov 2020
idx = sub2ind(size(A),2*i-1,2*i-1) ;
A(idx) = a(i) ;
You try to follow something like above.

#### 1 Comment

jyp on 25 Nov 2020
It works fine. Thanks.

R2019a

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