Fix error in volume element for ligo-skymap-stats

CHANGES.rst

@@ -13,6 +13,9 @@ Changelog
 - The ``bayestar-localize-lvalert`` and ``ligo-skymap-from-samples`` tools will
   now natively output multi-resolution HEALPix files.
 
+- Fix an error in the volume element that resulted in ``ligo-skymap-stats``
+  underestimating credible volumes by a factor of 2.
+
 0.0.17 (2018-10-24)
 ===================
 

ligo/skymap/postprocess/find_injection.py

@@ -228,7 +228,8 @@ def find_injection_moc(sky_map, true_ra=None, true_dec=None, true_dist=None,
 
         # Calculate volume of frustum-shaped voxels with distance centered on r
         # and extending from (r - d_r) to (r + d_r).
-        dV = (np.square(r) + np.square(d_r) / 12) * d_r * dA.reshape(-1, 1)
+        dV = (2 / 3 * (3 * np.square(r) + np.square(d_r))
+              * d_r * dA.reshape(-1, 1))
 
         # Calculate probability within each voxel.
         dP = probdensity.reshape(-1, 1) * dV * np.exp(