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.
