Specialize isdiag for KroneckerOperator (#344)

Author: jishnub

src/Operators/Operator.jl

@@ -549,6 +549,8 @@ macro wrappergetindex(Wrap)
             ApproxFunBase.mul_coefficients(view(parent(A).op,S.indexes[1],S.indexes[2]),b)
         ApproxFunBase.mul_coefficients(A::ApproxFunBase.SubOperator{T,OP},b) where {T,OP<:$Wrap} =
             ApproxFunBase.mul_coefficients(view(parent(A).op,S.indexes[1],S.indexes[2]),b)
+
+        isdiag(W::$Wrap) = isdiag(W.op)
     end
 
     for TYP in (:(ApproxFunBase.BandedMatrix),:(ApproxFunBase.RaggedMatrix),

src/PDE/KroneckerOperator.jl

@@ -105,7 +105,7 @@ end
 
 bandwidths(K::KroneckerOperator) = (ℵ₀,ℵ₀)
 
-for f in [:isblockbanded, :israggedbelow]
+for f in [:isblockbanded, :israggedbelow, :isdiag]
     _f = Symbol(:_, f)
     @eval begin
         $f(K::KroneckerOperator) = $(_f)(K.ops)