From 636b488890d4263e8dc0105121b85f70b8f2d19d Mon Sep 17 00:00:00 2001
From: Michael Ryan <mtryan83@gmail.com>
Date: Thu, 27 Jul 2023 13:17:31 -0400
Subject: [PATCH 1/3] Updates to the _parse_parameter_file function following
 PR 4470

---
 yt/frontends/gadget/data_structures.py | 37 +++++++++-----------------
 1 file changed, 12 insertions(+), 25 deletions(-)

diff --git a/yt/frontends/gadget/data_structures.py b/yt/frontends/gadget/data_structures.py
index e8ee428fcfa..a8bb0175c7a 100644
--- a/yt/frontends/gadget/data_structures.py
+++ b/yt/frontends/gadget/data_structures.py
@@ -363,24 +363,20 @@ def _parse_parameter_file(self):
         self.domain_dimensions = np.ones(3, "int32")
         self._periodicity = (True, True, True)
 
-        self.cosmological_simulation = 1
+        self.current_redshift = hvals.get("Redshift", 0.0)
+        if "Redshift" not in hvals:
+            mylog.info("Redshift is not set in Header. Assuming z=0.")
 
-        try:
-            self.current_redshift = hvals["Redshift"]
-        except KeyError:
-            # Probably not a cosmological dataset, we should just set
-            # z = 0 and let the user know
-            self.current_redshift = 0.0
-            only_on_root(mylog.info, "Redshift is not set in Header. Assuming z=0.")
-
-        try:
+        if "OmegaLambda" in hvals:
             self.omega_lambda = hvals["OmegaLambda"]
             self.omega_matter = hvals["Omega0"]
             self.hubble_constant = hvals["HubbleParam"]
-        except KeyError:
+            self.cosmological_simulation = self.omega_lambda != 0.0
+        else:
             # If these are not set it is definitely not a cosmological dataset.
             self.omega_lambda = 0.0
-            self.omega_matter = 1.0  # Just in case somebody asks for it.
+            self.omega_matter = 0.0  # Just in case somebody asks for it.
+            self.cosmological_simulation = 0
             # Hubble is set below for Omega Lambda = 0.
 
         # According to the Gadget manual, OmegaLambda will be zero for
@@ -389,12 +385,9 @@ def _parse_parameter_file(self):
         # which case we may be doing something incorrect here.
         # It may be possible to deduce whether ComovingIntegration is on
         # somehow, but opinions on this vary.
-        if self.omega_lambda == 0.0:
-            only_on_root(
-                mylog.info, "Omega Lambda is 0.0, so we are turning off Cosmology."
-            )
+        if not self.cosmological_simulation:
+            mylog.info("Omega Lambda is 0.0, so we are turning off Cosmology.")
             self.hubble_constant = 1.0  # So that scaling comes out correct
-            self.cosmological_simulation = 0
             self.current_redshift = 0.0
             # This may not be correct.
             self.current_time = hvals["Time"]
@@ -409,20 +402,14 @@ def _parse_parameter_file(self):
                 omega_lambda=self.omega_lambda,
             )
             self.current_time = cosmo.lookback_time(self.current_redshift, 1e6)
-            only_on_root(
-                mylog.info,
+            mylog.info(
                 "Calculating time from %0.3e to be %0.3e seconds",
                 hvals["Time"],
                 self.current_time,
             )
         self.parameters = hvals
 
-        prefix = os.path.abspath(
-            os.path.join(
-                os.path.dirname(self.parameter_filename),
-                os.path.basename(self.parameter_filename).split(".", 1)[0],
-            )
-        )
+        prefix = os.path.join(self.directory, self.basename.split(".", 1)[0])
 
         if hvals["NumFiles"] > 1:
             for t in (

From 3bc804b34fb4986f8d12ff03886f0931ca51f72a Mon Sep 17 00:00:00 2001
From: mtryan83 <mtrdraco@hotmail.com>
Date: Fri, 28 Jul 2023 11:54:47 -0400
Subject: [PATCH 2/3] Update yt/frontends/gadget/data_structures.py
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Clément Robert <cr52@protonmail.com>
---
 yt/frontends/gadget/data_structures.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/yt/frontends/gadget/data_structures.py b/yt/frontends/gadget/data_structures.py
index a8bb0175c7a..9192f2b0955 100644
--- a/yt/frontends/gadget/data_structures.py
+++ b/yt/frontends/gadget/data_structures.py
@@ -409,7 +409,8 @@ def _parse_parameter_file(self):
             )
         self.parameters = hvals
 
-        prefix = os.path.join(self.directory, self.basename.split(".", 1)[0])
+        basename, _, _ = self.basename.partition(".")
+        prefix = os.path.join(self.directory, basename)
 
         if hvals["NumFiles"] > 1:
             for t in (

From 20b5b59f40896ce13aa7f8087a1dbd419a00b67b Mon Sep 17 00:00:00 2001
From: Michael Ryan <mtryan83@gmail.com>
Date: Fri, 28 Jul 2023 18:49:08 -0400
Subject: [PATCH 3/3] Additional comment about change in omega_matter value

---
 yt/frontends/gadget/data_structures.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/yt/frontends/gadget/data_structures.py b/yt/frontends/gadget/data_structures.py
index 9192f2b0955..f7c828203d6 100644
--- a/yt/frontends/gadget/data_structures.py
+++ b/yt/frontends/gadget/data_structures.py
@@ -376,6 +376,8 @@ def _parse_parameter_file(self):
             # If these are not set it is definitely not a cosmological dataset.
             self.omega_lambda = 0.0
             self.omega_matter = 0.0  # Just in case somebody asks for it.
+            # omega_matter has been changed to 0.0 for consistency with
+            # non-cosmological frontends
             self.cosmological_simulation = 0
             # Hubble is set below for Omega Lambda = 0.