multiply desired indexes in for loop

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Othman Alkandri
Othman Alkandri 2022-12-28
评论： Voss 2022-12-28
I am trying to multiply the some indxes in my vector, bucuase there is a fctor I need to mutlipy it with the t vector of [ 1, 4,2,4,2,4,2 .........., 1].
  • frist index keep it
  • secound index multiply by 4
  • third index multiply by 2
  • forth index multiply by 4
  • fifth index multiply by 2
  • ..
  • ..
  • ..
  • last index keep it
t = [0.58 , 14.48, 19.91, 21.88, 22.59]
for i = 2:2:(length(t)-1)
A = 4*(t(i))+2*(t(i+1))
end
A = t(1)+A+t(end)

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采纳的回答

Voss
Voss 2022-12-28
编辑：Voss 2022-12-28
Ran in:
I think this is what you're going for:
t = [0.58 , 14.48, 19.91, 21.88, 22.59];
Nt = numel(t);
A = zeros(1,Nt);
for i = 2:2:(Nt-1)
A([i, i+1]) = [4*t(i), 2*t(i+1)];
end
A([1, end]) = t([1, end]);
disp(A);
0.5800 57.9200 39.8200 87.5200 22.5900
You can do the same thing like this:
t = [0.58 , 14.48, 19.91, 21.88, 22.59];
f = ones(1,numel(t)); % factors by which to multiply each element of t
f(2:2:end-1) = 4;
f(3:2:end-1) = 2;
A = f.*t;
disp(A);
0.5800 57.9200 39.8200 87.5200 22.5900

更多回答（1 个）

Image Analyst
Image Analyst 2022-12-28
Ran in:
I don't think your for loop does what you asked for in words. Here, try this to multiply a weights vector [1,4,2,4,2,4,......1] by a data vector t:
t = [0.58 , 14.48, 19.91, 21.88, 22.59];
numRepeats = length(t); % Number of times the pair [4,2] repeats.
% Make weights in the form [4,2,4,2,4,2,4,2,......];
weights = repmat([4,2], 1, numRepeats);
% That was too long, so let's crop it so we can multiply the vectors together.
% Also make the first and last element 1.
weights = [1, weights(1:length(t)-2), 1]; % [1,4,2,4,1] for this particular t.
% Now multiply the weights vector by the t vector element-by-element
A = t .* weights
A = 1×5
0.5800 57.9200 39.8200 87.5200 22.5900
Notice all the middle values are either 4 or 2 times the original values, in an alternating fashion.

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