use spdiagm in Serre-Green-Naghdi equations

Author: JoshuaLampert

src/DispersiveShallowWater.jl

@@ -33,7 +33,7 @@ import SciMLBase: u_modified!
 
 @reexport using StaticArrays: SVector
 using SimpleUnPack: @unpack
-using SparseArrays: sparse, issparse
+using SparseArrays: sparse, spdiagm, issparse
 using SummationByPartsOperators: SummationByPartsOperators,
                                  AbstractDerivativeOperator,
                                  PeriodicDerivativeOperator, PeriodicUpwindOperators,

src/equations/serre_green_naghdi_1d.jl

@@ -268,7 +268,7 @@ function assemble_system_matrix!(cache, h, D1, D1mat,
     # is not necessarily perfectly symmetric but only up to
     # round-off errors. We wrap it here to avoid issues with the
     # factorization.
-    return Symmetric(Diagonal(M_h) + D1mat' * Diagonal(M_h3_3) * D1mat)
+    return Symmetric(Diagonal(M_h) + D1mat' * spdiagm(M_h3_3) * D1mat)
 end
 
 # variable bathymetry