MATLAB: How to write sum

MATLABsigma notationsummation

How can I write this summation:

where N is simply input by the user

Simple !!

function Y=Summation(N)
Y=0;
for n=1:1:N
    Y=Y+((n+2)/sqrt(n))+n^3;
end
end

Done !!!

if length(P) and length(Y) is N:

x=sum(P.*Y)

in another case:

N=5; %set any value for N
x=sum(P(1:N).*Y(1:N))

I am a little confused, do you mean like this:

Y = reshape(1:18,6,3)  % A manageable dimension.
Y_1 = sum(Y,2)

So in your case it would be

Y_1 = sum(Y,2).';

Or do you mean, more like this:

Y = 1:18
Y_1 = sum(reshape(Y,3,6))

So in your case it would be

Y_1 = sum(reshape(Y,320,467))