Past exam of the year 1 of the computer science course of the University of Oxford / 2021 / Discrete mathematics, continuous mathematics, and probability / 6 / a / i / Solution

Write $r=x-a$. The squared Euclidean norm is $r^{T}r$, whose gradient is $2r$. The chain rule for the exponential function therefore gives the column gradientThe row derivative, if that convention is used for $df/dx$, is its transpose.