Question: Evaluate a sum with a vector input



I have a series as follows: 

b := (sum((x[i]-xbar)^3, i = 1 .. n))/(n*[(sum((x[i]-xbar)^2, i = 1 .. n))/(n-1)]^1.5)

(b is skewness of x)

Taking the derivatives:


c1:=diff(b, xbar);

c2:=diff(b, x[i]);

now I want to evaluate c1 and c2 with a matrix input:



where xbar is the mean value of x


Can you please help me








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