an Nx by Ny matrix passed to <code>sensor.directivity_angle</code>. These are assigned such that the maximum sensitivity of each sensor face faces inward.</p>

<pre class="codeinput">
<span class="comment">% define a four-sided, square sensor</span>
sensor.mask = zeros(kgrid.Nx, kgrid.Ny);
sensor.mask(1, :) = 1;
sensor.mask(end, :) = 1;
sensor.mask(:, 1) = 1;
sensor.mask(:, end) = 1;

<span class="comment">% run the simulation for omnidirectional detector elements</span>
sensor_data = kspaceFirstOrder2D(kgr