add box2cosmoredshift

csiborgtools/units/box_units.py

@@ -17,10 +17,11 @@ Simulation box unit transformations.
 """
 
 import numpy
-from astropy.cosmology import LambdaCDM
+from astropy.cosmology import (LambdaCDM, z_at_value)
 from astropy import (constants, units)
 from ..io import read_info
 
+
 # Map of unit conversions
 CONV_NAME = {
     "length": ["peak_x", "peak_y", "peak_z", "Rs", "rmin", "rmax", "r200",
@@ -198,6 +199,23 @@ class BoxUnits:
         """
         return self.box2kpc(length) * 1e-3
 
+    def box2cosmoredshift(self, length):
+        r"""
+        Convert the box comoving distance to cosmological redshift.
+
+        Parameters
+        ----------
+        length : float
+            Length in box units.
+
+        Returns
+        -------
+        cosmo_redshift : foat
+            The cosmological redshift.
+        """
+        dist = self.box2mpc(length) * units.Mpc
+        return z_at_value(self._cosmo.comoving_distance, dist)
+
     def solarmass2box(self, mass):
         r"""
         Convert mass from :math:`M_\odot` (with :math:`h=0.705`) to box units.