Remove extraneous post_explicit call

Author: charleskawczynski

src/solvers/imex_ark.jl

@@ -98,12 +98,12 @@ function step_u!(integrator, cache::IMEXARKCache)
 
         i ≠ 1 && dss!(U, p, t_exp)
 
-        if !(!isnothing(T_imp!) && !iszero(a_imp[i, i])) # Implicit solve
-            post_explicit!(U, p, t_imp)
-        else
+        if !(!isnothing(T_imp!) && !iszero(a_imp[i, i]))
+            i ≠ 1 && post_explicit!(U, p, t_imp)
+        else # Implicit solve
             @assert !isnothing(newtons_method)
             @. temp = U
-            post_explicit!(U, p, t_imp)
+            i ≠ 1 && post_explicit!(U, p, t_imp)
             # TODO: can/should we remove these closures?
             implicit_equation_residual! = (residual, Ui) -> begin
                 T_imp!(residual, Ui, p, t_imp)

src/solvers/imex_ssprk.jl

@@ -104,9 +104,9 @@ function step_u!(integrator, cache::IMEXSSPRKCache)
             end
         end
 
-        if !(!isnothing(T_imp!) && !iszero(a_imp[i, i])) # Implicit solve
-            post_explicit!(U, p, t_imp)
-        else
+        if !(!isnothing(T_imp!) && !iszero(a_imp[i, i]))
+            i ≠ 1 && post_explicit!(U, p, t_imp)
+        else # Implicit solve
             @assert !isnothing(newtons_method)
             @. temp = U
             post_explicit!(U, p, t_imp)