- Adds daily_growth and daily_growth_t instance attributes on Parameters class.

- Adds `daily_growth_helper` function to `src/penn_chime/parameters.py` to calculate daily growth rate as a function of doubling time.
- Updates `display_header` function in `src/penn_chime/presentation.py` to display initial and mitigated daily growth rates.
- Adds `test_daily_growth` test to `tests/test_app.py` to test above changes

Fixes #90

Author: Eric Smyth

src/penn_chime/parameters.py

@@ -4,7 +4,7 @@
 `change_date`, so users can see when results have last changed
 """
 
-from numpy import log2  # type: ignore
+from numpy import log2, power  # type: ignore
 
 from .utils import RateLos
 from .models import (
@@ -13,6 +13,10 @@
 )
 
 
+def daily_growth_helper(doubling_time):
+    return (power(2, 1.0 / doubling_time) - 1) * 100
+
+
 class Parameters:
     def __init__(
         self,
@@ -98,6 +102,9 @@ def __init__(
         if n_days is not None:
             self.n_days = n_days
 
+        self.daily_growth = daily_growth_helper(self.doubling_time)
+        self.daily_growth_t = power(2, 1.9 / self.doubling_time_t)
+
     @property
     def n_days(self):
         return self._n_days

src/penn_chime/presentation.py

@@ -60,10 +60,11 @@ def display_header(st, p):
     and Hospital market share (**{market_share:.0%}**).
 
 An initial doubling time of **{doubling_time}** days and a recovery time of **{recovery_days}** days imply an $R_0$ of
-**{r_naught:.2f}**.
+**{r_naught:.2f}** and daily growth rate of **{daily_growth:.2f}%**.
 
 **Mitigation**: A **{relative_contact_rate:.0%}** reduction in social contact after the onset of the
-outbreak reduces the doubling time to **{doubling_time_t:.1f}** days, implying an effective $R_t$ of **${r_t:.2f}$**.
+outbreak reduces the doubling time to **{doubling_time_t:.1f}** days, implying an effective $R_t$ of **${r_t:.2f}$** 
+and daily growth rate of **{daily_growth_t:.2f}%**.
 """.format(
             total_infections=p.infected,
             initial_infections=p.known_infected,
@@ -78,6 +79,8 @@ def display_header(st, p):
             relative_contact_rate=p.relative_contact_rate,
             r_t=p.r_t,
             doubling_time_t=p.doubling_time_t,
+            daily_growth=p.daily_growth,
+            daily_growth_t=p.daily_growth_t,
         )
     )
 

tests/test_app.py

@@ -71,6 +71,16 @@ def test_the_rest_of_header_shows_up():
     ), "The whole header should render"
 
 
+def test_daily_growth():
+    st.cleanup()
+    initial_growth = "and daily growth rate of **12.25%**."
+    mitigated_growth = "and daily growth rate of **1.18%**."
+    display_header(st, PARAM)
+    assert len((list(filter(lambda s: initial_growth in s, st.render_store))))
+    assert len((list(filter(lambda s: mitigated_growth in s, st.render_store))))
+    st.cleanup()
+
+
 st.cleanup()