Maybe a colon operator

Question

0 个投票

It is possible write this for in a more fast code (maybe colon)?

for i = 2 : n-1
  A(i) = A(i-1)+A(i+1);
end

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

Answer 1

Birdman 2017-11-28

1 个投票

Vectorizing is possible and better. One approach:

A=randi([1 10],1,10)
n=numel(A);
i=2:n-1;
A(i)=A(i-1)+A(i+1)

Answer 2

KSSV 2017-11-28

编辑：KSSV 2017-11-28

1 个投票

N = 10 ;
A = rand(N,1) ;
i = 2:N-1 ;
B = A(i-1)+A(i+1);

Jan 2017-11-28

编辑：Jan 2017-11-28

Note: If N is huge, creating the index vectors explicitly is slower than:

N = 1e7;
A = rand(N, 1) ;
B = A(1:(N-2)) + A(3:N);

Here Matlab checks only for the 4 given indices, if they are inside the valid range, while for

i = 2:N-1 ;
B = A(i-1) + A(i+1);

Matlab requires 2e7-4 boundary checks.