fix conversion to BandedMAtrix for coupling of one Legendre operator

Project.toml

@@ -1,7 +1,7 @@
 name = "SummationByPartsOperators"
 uuid = "9f78cca6-572e-554e-b819-917d2f1cf240"
 author = ["Hendrik Ranocha"]
-version = "0.4.0"
+version = "0.4.1"
 
 [deps]
 ArgCheck = "dce04be8-c92d-5529-be00-80e4d2c0e197"

src/banded_matrices.jl

@@ -30,7 +30,7 @@ function BandedMatrix(D::BandedDerivativeOperator)
         e[j] = 1
         mul!(dest, D, e)
         e[j] = 0
-        B.data[end-j-l+1:end,j] = dest[1:j+l]
+        B.data[end-j-l+1:end-j-l+min(j+l,length(e)),j] = dest[1:min(j+l,length(e))]
     end
     # inner part
     for j in max(l,u)+1:length(e)-max(l,u)
@@ -44,7 +44,8 @@ function BandedMatrix(D::BandedDerivativeOperator)
         e[j] = 1
         mul!(dest, D, e)
         e[j] = 0
-        B.data[1:length(e)+1-j+u,j] = dest[j-u:end]
+        # B.data[1:length(e)+1-j+u,j] = dest[j-u:end]
+        B.data[1+max(1,j-u)-(j-u):length(e)+1-j+u,j] = dest[max(1,j-u):end]
      end
 
     B

test/coupling_test.jl

@@ -36,9 +36,7 @@ using SummationByPartsOperators
           @test u ≈ v
           @test integrate(u, cD) ≈ sum(mass_matrix(cD) * u)
           @test integrate(u->u^2, u, cD) ≈ sum(u' * mass_matrix(cD) * u)
-          if N > 1
-            @test cD * u ≈ BandedMatrix(cD) * u
-          end
+          @test cD * u ≈ BandedMatrix(cD) * u
           @test cD * u ≈ Matrix(cD) * u
           @test cD * u ≈ sparse(cD) * u
         end