Add cosmological function between a and z

src/cosmology.c

@@ -639,6 +639,17 @@ double cosmology_get_delta_time(const struct cosmology *c,
   return t2 - t1;
 }
 
+
+/**
+ * @brief Compute the scale factor from the redshift.
+ *
+ * @brief c The current #cosmology.
+ * @brief redshift The redshift to compute.
+ */
+double cosmology_get_a_from_z(const struct cosmology *c, double redshift) {
+  return 1. / (1. + redshift);
+}
+
 /**
  * @brief Prints the #cosmology model to stdout.
  */

src/cosmology.h

@@ -180,6 +180,13 @@ double cosmology_get_therm_kick_factor(const struct cosmology *cosmo,
 double cosmology_get_delta_time(const struct cosmology *c,
                                 integertime_t ti_start, integertime_t ti_end);
 
+double cosmology_get_delta_time(const struct cosmology *c, double a1,
+                                double a2);
+
+double cosmology_get_a_from_z(const struct cosmology *c,
+			      double redshift);
+
+double cosmology_get_time_since_big_bang(const struct cosmology *c, double a);
 void cosmology_init(struct swift_params *params, const struct unit_system *us,
                     const struct phys_const *phys_const, struct cosmology *c);
 
@@ -188,6 +195,7 @@ void cosmology_init_no_cosmo(struct cosmology *c);
 void cosmology_print(const struct cosmology *c);
 void cosmology_clean(struct cosmology *c);
 
+
 #ifdef HAVE_HDF5
 void cosmology_write_model(hid_t h_grp, const struct cosmology *c);
 #endif