u t = d i v ( D ⋅ ∇ u ) {\displaystyle u_{t}=div(D\cdot \nabla u)} u ( x , t ) = { ( K 2 t ∗ f ) ( x ) , t > 0 {\displaystyle u(x,t)={\begin{cases}(K_{\sqrt {2t}}*f)(x),&t>0\end{cases}}} K σ {\displaystyle K_{\sigma }}
