Solution (source code)

= Solution

Solving the transformed <ordinary differential equation> with its <initial condition> gives $\widetilde\theta(k,t)=e^{-k^2t}\widetilde\theta(k,0)$. The <Fourier inversion theorem> therefore yields
$$
\boxed{\theta(x,t)=\frac1{2\pi}\int_{\mathbb R}e^{ikx-k^2t}\widetilde\theta(k,0)\,dk.}
$$
For $t>0$ the Gaussian multiplier suppresses large spatial frequencies, which explains the smoothing produced by <heat conduction>.