vectorise for loop with element wise multiplication

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;

Answer 1

[Ameer Hamza]

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

[madhan ravi]

If the OP is using an older version , PO might have to use bsxfun() for implicit expansion

[Muna Tageldin]

so what if I am trying to vectorize the following code :

a=[1;2;3;4;5]; b=[6;7;8;0;0]; c=[1;2;3;4;5];
z=zeros(5,5);
for i=1:5
    z(: , i)=a(i)*c(i)*exp(-b);
end

[Ameer Hamza]

Yes, on older versions, bxsfun will be used.

Muna, following is equivalent to your code

z = (a.'.*c.').*exp(-b)

[Muna Tageldin]

Great! Thanks