  For a standard graded ring $R$ of dimension $\geq 2$ over a perfect field of
characteristic $p>0$ and a homogeneous ideal $I$ of finite colength, the HK
density function of $R$ with respect to $I$ is a compactly supported continuous
function $f_{R, I}:[0, \infty)\longto [0, \infty)$, whose integration yields
the \mbox{HK} multiplicity $e_{HK}(R, I)$.
  Here we answer a question of V. Trivedi about the Hilbert-Kunz density
function of the tensor product of standard graded rings and show that it is the
convolution of the Hilbert-Kunz density function of the factor rings. Using
Fourier transform, as a corollary we get \mbox{HK} multiplicity of the tensor
product of rings is product of the HK multiplicity of the factor rings. We
compute the Fourier transform of the \mbox{HK} density function of a projective
curve.
