The following is a MATLAB function to calculate begin mathsize $20$px style sum from i equals $1$ to n of X subscript i end style, where n is the length of the vector begin mathsize $20$px style X with rightwards harpoon with barb upwards on top equals left square bracket X subscript $1$ comma space X subscript $2$ comma space... space comma space X subscript n right square bracket end style. Fill in the blank to complete the code. Do NOT type space in your answer. Note that MATLAB is case sensitive$.$

$===============$MATLAB CODE BEGIN$=================$

function s $=$ sumUp$($X$)$

$\%$ X is a vector here.

s $=0$;

for i $=1$:length$($X$)$

s $=$ s $+\_\_\_\_\_\_$;

end

end