GROMACS: emit the pressure that was already being parsed

gromacs.energy reads every term in the energies block into %term and then
emitted only the energy, so "Pressure (bar)" -- which GROMACS prints in
the same block, on the same line as Total Energy and Temperature -- was
parsed and thrown away.

Emitted from the existing [TE][TEVEC] entry rather than a new one.  The
marker line is byte-identical, and two .desc entries sharing a Begin
leave one of them permanently starved (PDMatchBegin returns only the
first match) -- the same reason TE and TEVEC already share this entry.

Units are Bar, which is what GROMACS labels the column and what
PressureConverter knows.  That is not cosmetic: convertTo() throws on an
unrecognised unit.

Scalar only, deliberately.  A per-step pressure would have to be a
PropTSVector<Geometry Step>, and GeomTracePropertyPanel plots any of
those against GEOMTRACE, which GROMACS has no producer for.  A
minimisation prints no pressure column at all, so the emission is
guarded and water_em legitimately has none.

The PRESSURE property itself came in with the Quantum ESPRESSO stress
work; this is its second consumer.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EFMUNbw2UpRPmgsqviAowb

Author: andy

scripts/parsers/gromacs.desc

@@ -55,7 +55,7 @@
 # apart. Parsed as a step it would put a final point on every
 # energy-vs-step plot whose value is an AVERAGE OVER THE RUN, and would
 # leave the scalar TE holding that average rather than the last step.
-[TE][TEVEC]
+[TE][TEVEC][PRESSURE]
 Script=gromacs.energy
 Begin=^\s*Energies \(kJ/mol\)
 Frequency=all

scripts/parsers/gromacs.energy

@@ -186,4 +186,29 @@ foreach my $k ("TE", "TEVEC") {
   print "units:\nkJoule/Mole\n";
   print "END\n";
 }
+
+#  Pressure comes out of the SAME block, already parsed into %term above,
+#  and is emitted from this one entry rather than a second .desc entry --
+#  the marker line is identical, and two entries sharing a Begin would
+#  leave one of them permanently starved (PDMatchBegin returns only the
+#  first match).
+#
+#  GROMACS labels the column "Pressure (bar)", and bar is a unit
+#  PressureConverter knows.  That matters: convertTo() THROWS on a unit
+#  it does not have, so an invented label would be an exception rather
+#  than a cosmetic wart.
+#
+#  Scalar only, deliberately.  A per-step pressure would have to be a
+#  PropTSVector<Geometry Step>, and GeomTracePropertyPanel plots any of
+#  those against GEOMTRACE -- which GROMACS has no producer for, so the
+#  trace would be unplottable at best and out of bounds at worst (the
+#  len(TEVEC) <= len(GEOMTRACE) rule in CLAUDE.md).  A minimisation run
+#  prints no pressure at all, hence the defined() guard.
+if (defined($term{"Pressure (bar)"})) {
+  print "key: PRESSURE\n";
+  print "size:\n1\n";
+  print "values:\n" . $term{"Pressure (bar)"} . "\n";
+  print "units:\nBar\n";
+  print "END\n";
+}
 exit(0);

tests/parsers/cases.py

@@ -1133,7 +1133,10 @@
         fixture='gromacs/water_em.log',
         parse_args=('.', 'Energy', 'MD', 'OPLS', '0'),
         expect={
-            'TE][TEVEC': dict(blocks=5, keys={
+            #  A minimisation prints no pressure column at all, so
+            #  PRESSURE is absent here by design -- the parser guards on
+            #  the term being present rather than emitting an empty one.
+            'TE][TEVEC][PRESSURE': dict(blocks=5, keys={
                 'TE': {'values': '-8.19803e+03', 'units': 'kJoule/Mole'},
                 'TEVEC': {'units': 'kJoule/Mole'}}),
         },
@@ -1163,9 +1166,13 @@
             #  [NULL] suppressor ever stops swallowing it, TE lands on
             #  the run average and this fails loudly instead of quietly
             #  reporting a plausible wrong number.
-            'TE][TEVEC': dict(blocks=6, keys={
+            'TE][TEVEC][PRESSURE': dict(blocks=6, keys={
                 'TE': {'values': '-7.11568e+03', 'units': 'kJoule/Mole'},
-                'TEVEC': {'units': 'kJoule/Mole'}}),
+                'TEVEC': {'units': 'kJoule/Mole'},
+                #  Same argument as TE: the LAST STEP's pressure, not the
+                #  averages block's. Units must be one PressureConverter
+                #  knows -- it throws on anything else.
+                'PRESSURE': {'values': '-2.13868e+03', 'units': 'Bar'}}),
         },
     ),
     dict(

tests/parsers/expected/gromacs-water-em.txt

@@ -4,7 +4,7 @@ desc:    gromacs.desc
 fixture: gromacs/water_em.log (472 lines)
 args:    '.' 'Energy' 'MD' 'OPLS' '0'
 
-[TE][TEVEC]  Script=gromacs.energy  Freq=all  Skip=0  Lines=-
+[TE][TEVEC][PRESSURE]  Script=gromacs.energy  Freq=all  Skip=0  Lines=-
   Begin=^\s*Energies \(kJ/mol\)
   End=^\s*$
   begins=5 delivered=5 buffered_away=0
@@ -17,6 +17,10 @@ args:    '.' 'Energy' 'MD' 'OPLS' '0'
       size: 1
       values: -1.99051e+03
       units: kJoule/Mole
+    key: PRESSURE
+      size: 1
+      values: 4.93577e+04
+      units: Bar
   block 2: begin-line=435 fed=4 rc=0 first-fed='   Energies (kJ/mol)'
     key: TE
       size: 1
@@ -26,6 +30,10 @@ args:    '.' 'Energy' 'MD' 'OPLS' '0'
       size: 1
       values: -5.73156e+03
       units: kJoule/Mole
+    key: PRESSURE
+      size: 1
+      values: 1.72969e+04
+      units: Bar
   block 3: begin-line=442 fed=4 rc=0 first-fed='   Energies (kJ/mol)'
     key: TE
       size: 1
@@ -35,6 +43,10 @@ args:    '.' 'Energy' 'MD' 'OPLS' '0'
       size: 1
       values: -7.16623e+03
       units: kJoule/Mole
+    key: PRESSURE
+      size: 1
+      values: 5.66364e+03
+      units: Bar
   block 4: begin-line=449 fed=4 rc=0 first-fed='   Energies (kJ/mol)'
     key: TE
       size: 1
@@ -44,6 +56,10 @@ args:    '.' 'Energy' 'MD' 'OPLS' '0'
       size: 1
       values: -7.67943e+03
       units: kJoule/Mole
+    key: PRESSURE
+      size: 1
+      values: 1.82489e+03
+      units: Bar
   block 5: begin-line=456 fed=4 rc=0 first-fed='   Energies (kJ/mol)'
     key: TE
       size: 1
@@ -53,4 +69,8 @@ args:    '.' 'Energy' 'MD' 'OPLS' '0'
       size: 1
       values: -8.19803e+03
       units: kJoule/Mole
+    key: PRESSURE
+      size: 1
+      values: -1.66600e+03
+      units: Bar
 

tests/parsers/expected/gromacs-water-md.txt

@@ -4,7 +4,7 @@ desc:    gromacs.desc
 fixture: gromacs/water_md.log (612 lines)
 args:    '.' 'Dynamics' 'MD' 'OPLS' '0'
 
-[TE][TEVEC]  Script=gromacs.energy  Freq=all  Skip=0  Lines=-
+[TE][TEVEC][PRESSURE]  Script=gromacs.energy  Freq=all  Skip=0  Lines=-
   Begin=^\s*Energies \(kJ/mol\)
   End=^\s*$
   begins=6 delivered=6 buffered_away=0
@@ -17,6 +17,10 @@ args:    '.' 'Dynamics' 'MD' 'OPLS' '0'
       size: 1
       values: -8.18669e+03
       units: kJoule/Mole
+    key: PRESSURE
+      size: 1
+      values: -1.63353e+03
+      units: Bar
   block 2: begin-line=468 fed=6 rc=0 first-fed='   Energies (kJ/mol)'
     key: TE
       size: 1
@@ -26,6 +30,10 @@ args:    '.' 'Dynamics' 'MD' 'OPLS' '0'
       size: 1
       values: -7.33732e+03
       units: kJoule/Mole
+    key: PRESSURE
+      size: 1
+      values: -2.89873e+03
+      units: Bar
   block 3: begin-line=477 fed=6 rc=0 first-fed='   Energies (kJ/mol)'
     key: TE
       size: 1
@@ -35,6 +43,10 @@ args:    '.' 'Dynamics' 'MD' 'OPLS' '0'
       size: 1
       values: -7.19592e+03
       units: kJoule/Mole
+    key: PRESSURE
+      size: 1
+      values: -1.50656e+03
+      units: Bar
   block 4: begin-line=486 fed=6 rc=0 first-fed='   Energies (kJ/mol)'
     key: TE
       size: 1
@@ -44,6 +56,10 @@ args:    '.' 'Dynamics' 'MD' 'OPLS' '0'
       size: 1
       values: -7.14458e+03
       units: kJoule/Mole
+    key: PRESSURE
+      size: 1
+      values: -2.07738e+03
+      units: Bar
   block 5: begin-line=495 fed=6 rc=0 first-fed='   Energies (kJ/mol)'
     key: TE
       size: 1
@@ -53,6 +69,10 @@ args:    '.' 'Dynamics' 'MD' 'OPLS' '0'
       size: 1
       values: -7.18100e+03
       units: kJoule/Mole
+    key: PRESSURE
+      size: 1
+      values: -2.89189e+03
+      units: Bar
   block 6: begin-line=507 fed=6 rc=0 first-fed='   Energies (kJ/mol)'
     key: TE
       size: 1
@@ -62,6 +82,10 @@ args:    '.' 'Dynamics' 'MD' 'OPLS' '0'
       size: 1
       values: -7.11568e+03
       units: kJoule/Mole
+    key: PRESSURE
+      size: 1
+      values: -2.13868e+03
+      units: Bar
 
 [NULL]  Script=gromacs.null  Freq=last  Skip=0  Lines=-
   Begin=A V E R A G E S