Read values of z for z views

I have a nonlinear problem I want to solve matrix free (using appropriate Newton and solver backends from exadune) that didn't run. I tried numerical differentation and implementing jacobian_apply.

Looking through PDELab led to this (potential) bug that solves the issue for me. It looked suspicious so I tried the change but for my own sanity I didn't think further about it after going through all this engine stuff ;). Because of that I'm not sure if this is really a bug or if my problems can be found elsewhere. Should be merged with care.

dune/pdelab/gridoperator/default/nonlinearjacobianapplyengine.hh

@@ -201,12 +201,12 @@ namespace Dune{
       template<typename LFSUC>
       void loadCoefficientsLFSUInside(const LFSUC & lfsu_s_cache){
         global_sl_view.read(xl);
-        global_zl_view.read(xl);
+        global_zl_view.read(zl);
       }
       template<typename LFSUC>
       void loadCoefficientsLFSUOutside(const LFSUC & lfsu_n_cache){
         global_sn_view.read(xn);
-        global_zn_view.read(xn);
+        global_zn_view.read(zn);
       }
       template<typename LFSUC>
       void loadCoefficientsLFSUCoupling(const LFSUC & lfsu_c_cache)
@@ -256,7 +256,7 @@ namespace Dune{
         Dune::PDELab::LocalAssemblerCallSwitch<LOP,LOP::doAlphaSkeleton>::
           nonlinear_jacobian_apply_skeleton(lop,ig,
                                             lfsu_s_cache.localFunctionSpace(),xl,zl,lfsv_s_cache.localFunctionSpace(),
-                                            lfsu_n_cache.localFunctionSpace(),xn,zl,lfsv_n_cache.localFunctionSpace(),
+                                            lfsu_n_cache.localFunctionSpace(),xn,zn,lfsv_n_cache.localFunctionSpace(),
                                             rl_view,rn_view);
       }