fix error

Author: Ig-dolci

gusto/equations/boussinesq_equations.py

@@ -173,8 +173,10 @@ def __init__(self, domain, parameters,
         # -------------------------------------------------------------------- #
         if compressible:
             cs = parameters.cs
+            # On assuming ``cs`` as a constant, it is right keep it out of the
+            # integration.
             linear_div_form = divergence(subject(
-                prognostic(cs**2 * phi * div(u_trial) * dx, 'p'), self.X))
+                prognostic(cs**2 * (phi * div(u_trial) * dx), 'p'), self.X))
             divergence_form = divergence(linearisation(
                 subject(prognostic(cs**2 * phi * div(u) * dx, 'p'), self.X),
                 linear_div_form))

gusto/equations/shallow_water_equations.py

@@ -169,8 +169,9 @@ def _setup_residual(self, fexpr, topog_expr, u_transport_option):
         # -------------------------------------------------------------------- #
         # Pressure Gradient Term
         # -------------------------------------------------------------------- #
+        # On assuming ``g``, it is right to keep it out of the integral.
         pressure_gradient_form = pressure_gradient(
-            subject(prognostic(-g*div(w)*D*dx, 'u'), self.X))
+            subject(prognostic(-g*(div(w)*D*dx), 'u'), self.X))
 
         residual = (mass_form + adv_form + pressure_gradient_form)