Adding Array elements from one element to another

I have an array that contains all of my power values in dBm from a LoRa signal. I found the 10dB bandwidth (BW) but I want to add the elements from one point in the array to another point.

My array has 1,000,000 elements and I want to add the elements from element 487146 to element 513795 in my array to find the total power im looking for. What advice could you give? I have tried sum but not sure have to implement it in this case

Answer 1

[KSSV]

Let A be your array.

iwant = sum(A(487146:513795)) ; 

[Charith Ranatunga]

Sweet thank you, I got it working I just used the 'abs' function cause I got a negative total power value between those elements