From a4fb14dbc20cd258920a8dc438d21baef2ef1bc1 Mon Sep 17 00:00:00 2001
From: Joe Zuntz <joezuntz@googlemail.com>
Date: Fri, 12 Jul 2024 10:43:39 +0200
Subject: [PATCH] add CMB shift parameter calculation to camb

---
 boltzmann/camb/camb_interface.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/boltzmann/camb/camb_interface.py b/boltzmann/camb/camb_interface.py
index 14e39c78..305982fc 100644
--- a/boltzmann/camb/camb_interface.py
+++ b/boltzmann/camb/camb_interface.py
@@ -20,6 +20,7 @@
 
 DEFAULT_A_S = 2.1e-9
 
+C_KMS = 299792.458
 
 # See this table for description:
 #https://camb.readthedocs.io/en/latest/transfer_variables.html#transfer-variables
@@ -430,6 +431,9 @@ def save_derived_parameters(r, block):
     for k, v in derived.items():
         block[names.distances, k] = v
     block[names.distances, 'rs_zdrag'] = block[names.distances, 'rdrag']
+    zstar = derived['zstar']
+    shift = r.angular_diameter_distance(zstar) * (1 + zstar) * (p.omegam * p.H0**2)**0.5 / C_KMS
+    block[names.distances, "cmbshift"] = shift
     
     p.omegal = 1 - p.omegam - p.omk
     p.ommh2 = p.omegam * p.h**2