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March 25th, 2017, 11:14 AM   #1
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A Q on mulplying two vectors in Matlab

Hi--I have two vectors $\displaystyle x = (x_1, x_2, ..., x_n)$ and $\displaystyle y = (y_1, y_2, ..., y_n)$.

Now I want them to be multiplied in the following way: for each $\displaystyle i=1,2,..,n$, I need $\displaystyle x_i * y_{i-1}-y_n$.

Can anyone help me on how to code this in Matlab?

BTW, I also want to input the length of the two vectors "n" at the very beginning of the program. What do I need to do in order ensure the lengths of vectors $\displaystyle x$ and $\displaystyle y$ are the "n" I specified as an input?

Thanks in advance!
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March 25th, 2017, 03:01 PM   #2
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You can assign n to be whatever you want, then in your for loop, loop from i = 1:n, and then compute your sums. This will ensure that their lengths are n.
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March 25th, 2017, 06:46 PM   #3
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Is there anyway to use Matrix, rather than loop? Thanks.
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March 25th, 2017, 07:17 PM   #4
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Hmm.. Not efficiently no?

If you want to compute your function for every value of i, then the best way would be to store those values in a matrix. Something like,

for i = 1:n
$\qquad$storage_mat(i) = x(i) * y(i-1) - y(i);
end

Where i is the index and your storage matrix would be something like,

storage_mat(1:n) = [x(1)*y(0) - y(1), x(2)*y(1) - y(2), ..., x(n)*y(n - 1) - y(n)]

Of course you will need to do some setting up before the for loop, and pay careful attention to your indexing in matlab (i.e., the first element in an array is 1, not zero).
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