d</span>
ppw = medium.sound_speed / (freq * dx); <span class="comment">% points per wavelength</span>
cfl = 0.3;                              <span class="comment">% cfl number</span>
ppp = ceil(ppw / cfl);                  <span class="comment">% points per period</span>
T   = 1 / freq;                         <span class="comment">% period [s]</span>
dt  = T / ppp;                          <span class="comment">% time step [s]</span>
</pre>

<p>Here, the acoustic source is defined to be a focused transduc