make helpers.jump() do nothing if not assembled through asm()

docs/examples/ex07.py

@@ -12,23 +12,23 @@
 bb = FacetBasis(m, e)
 fb = [InteriorFacetBasis(m, e, side=i) for i in [0, 1]]
 
+
 @BilinearForm
-def dgform(u, v, p):
-    ju, jv = jump(p, u, v)
-    h = p.h
-    n = p.n
+def dgform(u, v, w):
+    ju, jv = jump(w, u, v)
+    h = w.h
+    n = w.n
     return ju * jv / (alpha * h) - dot(grad(u), n) * jv - dot(grad(v), n) * ju
 
-@BilinearForm
-def nitscheform(u, v, p):
-    h = p.h
-    n = p.n
-    return u * v / (alpha * h) - dot(grad(u), n) * v - dot(grad(v), n) * u
 
-A = asm(laplace, ib)
+A = laplace.assemble(ib)
+C = dgform.assemble(bb)
+b = unit_load.assemble(ib)
+
+# calling asm(form, [...], [...]) will automatically
+# assemble all combinations from the lists and sum
+# the result
 B = asm(dgform, fb, fb)
-C = asm(nitscheform, bb)
-b = asm(unit_load, ib)
 
 x = solve(A + B + C, b)
 

skfem/helpers.py

@@ -12,8 +12,7 @@
 
 def jump(w: FormExtraParams, *args):
     if not hasattr(w, 'idx'):
-        raise NotImplementedError("jump() can be used only if the form is "
-                                  "assembled through asm().")
+        return args
     out = []
     for i, arg in enumerate(args):
         out.append((-1.) ** w.idx[i] * arg)