fix 5-arg mul! with empty lower coefficients of periodic operators (#212

)

* fix 5-arg mul! with empty lower coefficients of periodic operators

* bump version

Project.toml

@@ -1,7 +1,7 @@
 name = "SummationByPartsOperators"
 uuid = "9f78cca6-572e-554e-b819-917d2f1cf240"
 author = ["Hendrik Ranocha"]
-version = "0.5.44"
+version = "0.5.45"
 
 [deps]
 ArgCheck = "dce04be8-c92d-5529-be00-80e4d2c0e197"

src/periodic_operators.jl

@@ -82,11 +82,15 @@ end
 
     ex_upper = :( nothing )
     for i in (UpperOffset-1):-1:0
-        ex = :( lower_coef[$LowerOffset]*u[end-$(i+LowerOffset)] )
-        for j in LowerOffset-1:-1:1
-            ex = :( $ex + lower_coef[$j]*u[end-$(j+i)] )
+        if LowerOffset > 0
+            ex = :( lower_coef[$LowerOffset]*u[end-$(i+LowerOffset)] )
+            for j in LowerOffset-1:-1:1
+                ex = :( $ex + lower_coef[$j]*u[end-$(j+i)] )
+            end
+            ex = :( $ex + central_coef*u[end-$i] )
+        else
+            ex = :( central_coef*u[end-$i] )
         end
-        ex = :( $ex + central_coef*u[end-$i] )
         for j in 1:UpperOffset
             if i-j < 0
                 ex = :( $ex + upper_coef[$j]*u[$(j-i)] )

test/upwind_operators_test.jl

@@ -103,3 +103,26 @@ end
     derivative_operator(Mattsson2017(:plus   ), 1, acc_order, xmin, xmax, N)
   )
 end
+
+@testset "Empty lower/upper coefficients" begin
+  D = upwind_operators(periodic_derivative_operator, accuracy_order = 2,
+                       xmin = 0.0, xmax = 1.0, N = 10)
+  x = grid(D)
+  u = @. sinpi(2 * x)
+
+  du = zero(u)
+  @test_nowarn mul!(du, D.minus, u)
+  @test du ≈ D.minus * u
+  @test_nowarn mul!(du, D.minus, u, 2.0)
+  @test du ≈ 2 * D.minus * u
+  @test_nowarn mul!(du, D.minus, u, 2.0, 3.0)
+  @test du ≈ 8 * D.minus * u # 5 = 2 + 3 * 2
+
+  du = zero(u)
+  @test_nowarn mul!(du, D.plus, u)
+  @test du ≈ D.plus * u
+  @test_nowarn mul!(du, D.plus, u, 2.0)
+  @test du ≈ 2 * D.plus * u
+  @test_nowarn mul!(du, D.plus, u, 2.0, 3.0)
+  @test du ≈ 8 * D.plus * u # 5 = 2 + 3 * 2
+end