MATLAB: Vectorise for loop with element wise multiplication

for loopvectorization

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;

Best Answer

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
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