vectorise for loop with element wise multiplication
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Muna Tageldin
le 21 Sep 2020
Commenté : Muna Tageldin
le 22 Sep 2020
I have this code that I am trying to vectorize with for loop
the function is very complicated so a simplified version is
f=@(a,b) a.exp(-b);
a and b of the same size
(a=[1;2;3;4;5]; b=[6;7;8;0;0]
)
so the for loop that I am trying to vectorize is this:
z=zeros(5,5)
for i=1:5
z(: , i)=a(i)*exp(-b);
end
I am interested in having this matrix:
z=[a(1)*exp(-b) , a(2)*exp(-b) ,a(3)*exp(-b), a(4)*exp(-b) , a(5)*exp(-b) ];
The aim is to vectorise this code so faster computation is achieved
I tried using bsxfun;
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Ameer Hamza
le 21 Sep 2020
Modifié(e) : Ameer Hamza
le 21 Sep 2020
Loops are not always necessarily slow. However, the vectorized code is much more cleaner and readable. For the simple example, you can use automatic array expansion introduced in some recent release of MATLAB. The following two code are equivalent.
a=[1;2;3;4;5]; b=[6;7;8;0;0];
z=zeros(5,5);
for i=1:5
z(: , i)=a(i)*exp(-b);
end
and
a=[1;2;3;4;5]; b=[6;7;8;0;0];
z = a.'.*exp(-b); % note a is used as a row vector and b is used as a column vector
4 commentaires
Ameer Hamza
le 22 Sep 2020
Yes, on older versions, bxsfun will be used.
Muna, following is equivalent to your code
z = (a.'.*c.').*exp(-b)
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