Bugfix: Corrected handling of viscosity <= 0.0

HISTORY.rst

@@ -1,6 +1,11 @@
 =======
 History
 =======
+2026.3.26 -- Bugfix: Corrected handling of viscosity <= 0.0
+    * Ignore the hydrostatic correction if the given viscosity is less than or equal
+      to 0. This allows a flowchart to work more simply whether the viscosity os know or
+      not.
+
 2026.3.15 -- Fixed an error with MLFFs and protected the viscosity correction.
     * Fixed and error with the name of the MLFF, which caused the code to crash after
       printing the results but before ending.

diffusivity_step/diffusivity.py

@@ -1027,7 +1027,7 @@ def analyze(
 
         # If requested, calculate the Yeh-Hummer correction for cell size
         correction = None
-        if P["hydrodynamic correction"]:
+        if P["hydrodynamic correction"] and P["viscosity"] > 0:
             if "T" in self._state_vars:
                 T = self._state["T"][-1]
                 if "a" in self._state_vars:
@@ -1164,12 +1164,19 @@ def description_text(self, P=None, short=False):
             )
 
         correction = P["hydrodynamic correction"]
+        viscosity = P["viscosity"]
+        if not self.is_expr(viscosity):
+            try:
+                if viscosity.magnitude <= 0:
+                    correction = "no"
+            except Exception:
+                pass
 
         if isinstance(correction, str) and self.is_expr(correction):
             text += (
                 f" The expression '{correction}' will determine whether to use the "
                 "Yeh-Hummer hydrodynamic correction for the finite cell size using "
-                f"a viscosity of {P['viscosity']}."
+                f"a viscosity of {viscosity}."
             )
         else:
             if isinstance(correction, str):
@@ -1178,7 +1185,7 @@ def description_text(self, P=None, short=False):
                 text += (
                     " The calculated diffusivity will be corrected for the finite cell "
                     "size using the Yeh-Hummer hydrodynamic correction using "
-                    f"a viscosity of {P['viscosity']}."
+                    f"a viscosity of {viscosity}."
                 )
 
         text += "\n\n"