how to find the value at mid of the indices

Actually I need to find this sum with value of Y at (j+1/2)

Rsum1=0;

for j=1:1:n+1

Rsum1=Rsum1+aa(j)*Y(j)

end

so how to do it?

[Durganshu]

Your problem description is not clear.

'Actually I need to find this sum with value of Y at (j+1/2)'

If Y contains n+1 values and each value is stored at an index that varies with an interval of j=1, how will we be able to extract the values at the intermediate indexes (j+1/2)?

Also, what exactly is aa(j)?

Elaborate more on what you exactly need and if possible, provode with sample inputs and outputs.