Fix the electrolyzer example and remove an unused part in fluid vecto…

…r presolving (for now)

src/tespy/components/reactors/water_electrolyzer.py

@@ -176,10 +176,10 @@ class WaterElectrolyzer(Component):
     >>> round(el.eta.val, 1)
     0.8
     >>> el_cmp.set_attr(v=None)
-    >>> el.set_attr(P=P_design * 0.66)
+    >>> el.set_attr(P=P_design * 1e6 * 0.2)
     >>> nw.solve('offdesign', design_path='tmp')
     >>> round(el.eta.val, 2)
-    0.88
+    0.84
     >>> shutil.rmtree('./tmp', ignore_errors=True)
     """
 

src/tespy/networks/network.py

@@ -1109,9 +1109,11 @@ def presolve_fluid_topology(self):
                 main_conn.fluid.val.update(fixed_fractions)
                 main_conn.fluid.is_set = {f for f in fixed_fractions}
                 main_conn.fluid.is_var = variable
-                num_var = len(variable)
-                for f in variable:
-                    main_conn.fluid.val[f] = (1 - mass_fraction_sum) / num_var
+                # this seems to be a problem in some cases, e.g. the basic
+                # gas turbine tutorial
+                # num_var = len(variable)
+                # for f in variable:
+                #     main_conn.fluid.val[f] = (1 - mass_fraction_sum) / num_var
 
             [c.build_fluid_data() for c in all_connections]
             for fluid in main_conn.fluid.is_var: