# Vectorize the loops within the function

1 view (last 30 days)
AM on 12 Feb 2020
Commented: AM on 19 Feb 2020
Hi, I am trying to create a function for Lagrange's interpolation and I wanted to know if there is a way to vectorize it that makes the code run faster
function y=lagrange(xx,yy,x)
% xx and yy are vectors of data values, x is the vector I want to interpolate
n=size(xx,2);
y=zeros(1,length(x));
for k=1:length(x)
for i=1:n
L=1;
for j =1:n
if j~=i
L=L*(x(k)-xx(j))/(xx(i)-xx(j));
end
end
y(k) =y(k)+yy(i)*L;
end
end
end
I tried to do the following but the code is actually slower
for k=1:length(x)
for i=1:n
j=1:n;j(j==i)=[];
L=prod((x(k)-xx(j))./(xx(i)-xx(j)));
y(k) =y(k)+yy(i)*L;
end
end
Any help is appreciated, thank you!
darova on 12 Feb 2020
Vectorized code is not always faster
Sometimes code is more readable with for loops
AM on 19 Feb 2020
I see, thank you!

Srivardhan Gadila on 18 Feb 2020
In line 3 of the vectorized code, replace 'j(j==i)=[];' with 'j(i) = [ ];' as it takes time for finding i, which in this case is not needed and also consider declaring any fixed array before itself and not inside for loops.
n=size(xx,2);
y=zeros(1,length(x));
nvec = 1:n;
for k=1:length(x)
for i= nvec
j=nvec;j(i)=[];
y(k) =y(k)+yy(i)*prod((xx(j)-x(k))./(xx(j)-xx(i)));
end
end
Vectorized code often runs much faster than the corresponding code containing loops but not always. Please refer to the following for more information Vectorization.

### Categories

Find more on Resizing and Reshaping Matrices in Help Center and File Exchange

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!