Euler's “mixed” initial condition for <a href="https://en.wikipedia.org/wiki/wave_equation" class="extiw" title="en:wave equation">vibrating string equation</a>
<a href="//commons.wikimedia.org/wiki/User:Ilya_Voyager" title="User:Ilya Voyager">Ilya Voyager</a>
<span class="int-own-work" lang="en">Own work</span>