fix scalar flux time derviatve scaling

yardasol · yardasol · commit 774fb9b7302b · 2026-04-07T13:53:42.000-05:00
diff --git a/src/random_ray/flat_source_domain.cpp b/src/random_ray/flat_source_domain.cpp
@@ -2022,7 +2022,8 @@ void FlatSourceDomain::compute_single_phi_prime(SourceRegionHandle& srh)
 
     double scalar_flux_time_derivative =
       A0 * srh.scalar_flux_old(g) + srh.scalar_flux_rhs_bd(g);
-    srh.phi_prime(g) = scalar_flux_time_derivative * inverse_vbar / sigma_t;
+    srh.phi_prime(g) =
+      scalar_flux_time_derivative * inverse_vbar / (4 * PI * sigma_t);
   }
 }
 
@@ -2049,7 +2050,7 @@ void FlatSourceDomain::compute_single_T1(SourceRegionHandle& srh)
 
     double scalar_flux_time_derivative_2 =
       B0 * srh.scalar_flux_old(g) + srh.scalar_flux_rhs_bd_2(g);
-    scalar_flux_time_derivative_2 *= inverse_vbar;
+    scalar_flux_time_derivative_2 *= inverse_vbar / (4 * PI);
 
     // Divide by sigma_t to save time during transport
     srh.T1(g) =

Original file line number	Diff line number	Diff line change
`@@ -2022,7 +2022,8 @@ void FlatSourceDomain::compute_single_phi_prime(SourceRegionHandle& srh)`
`2022`	`2022`
`2023`	`2023`	`double scalar_flux_time_derivative =`
`2024`	`2024`	`A0 * srh.scalar_flux_old(g) + srh.scalar_flux_rhs_bd(g);`
`2025`		`- srh.phi_prime(g) = scalar_flux_time_derivative * inverse_vbar / sigma_t;`
	`2025`	`+ srh.phi_prime(g) =`
	`2026`	`+ scalar_flux_time_derivative * inverse_vbar / (4 * PI * sigma_t);`
`2026`	`2027`	`}`
`2027`	`2028`	`}`
`2028`	`2029`
`@@ -2049,7 +2050,7 @@ void FlatSourceDomain::compute_single_T1(SourceRegionHandle& srh)`
`2049`	`2050`
`2050`	`2051`	`double scalar_flux_time_derivative_2 =`
`2051`	`2052`	`B0 * srh.scalar_flux_old(g) + srh.scalar_flux_rhs_bd_2(g);`
`2052`		`- scalar_flux_time_derivative_2 *= inverse_vbar;`
	`2053`	`+ scalar_flux_time_derivative_2 = inverse_vbar / (4 PI);`
`2053`	`2054`
`2054`	`2055`	`// Divide by sigma_t to save time during transport`
`2055`	`2056`	`srh.T1(g) =`