Fix bug in VMECIO.write_vmec_input (#1667)

- Adds missing `&END` to the input file created from
`desc.vmec.VMECIO.write_vmec_input`, and adds automatically generated
header file showing date the input file was created.

Resolves #1653

Author: dpanici

CHANGELOG.md

@@ -2,10 +2,10 @@ Changelog
 =========
 
 New Features
-
 - Adds a new utility function ``desc.compat.contract_equilibrium`` which takes in an ``Equilibrium`` object and an argument ``inner_rho``, and returns a new ``Equilibrium`` with original ``Equilibrium``'s ``inner_rho`` flux surface as its boundary.
 Optionally can also contract the profiles of the original ``Equilibrium`` so that the new ``Equilibrium``'s profiles match the original's in real space.
 - Adds second-order NAE constraints, accessible by passing ``order=2`` to ``desc.objectives.get_NAE_constraints``.
+- Adds automatically generated header file showing date the input file was created with `desc.vmec.VMECIO.write_vmec_input`
 
 
 v0.14.1
@@ -15,6 +15,7 @@ Bug Fixes
 - Fixes bug in ``desc.vmec.VMECIO.write_vmec_input`` for current-constrained equilibria, where DESC was incorrectly writing the ``s**0`` mode, where VMEC actually assumes it is zero and starts at the  ``s**1`` (which is different than the usual convention VMEC uses for its current profile when it uses the current derivative, where it starts with the ``s**0`` mode).
 - Fixes error that occurs when using the default grid for ``SplineXYZCoil`` in an optimization.
 - Fixes bug in ``desc.coils.CoilSet.save_in_makegrid_format`` for ``CoilSet`` objects with ``sym=True`` or ``NFP>1``
+- Adds missing `&END` to the input file created from `desc.vmec.VMECIO.write_vmec_input`
 
 v0.14.0
 -------

desc/vmec.py

@@ -3,13 +3,15 @@
 import io
 import os
 import warnings
+from datetime import datetime
 
 import matplotlib.pyplot as plt
 import numpy as np
 from netCDF4 import Dataset, stringtochar
 from scipy import integrate, interpolate, optimize
 from scipy.constants import mu_0
 
+import desc
 from desc.basis import DoubleFourierSeries
 from desc.compat import ensure_positive_jacobian
 from desc.equilibrium import Equilibrium
@@ -1432,7 +1434,7 @@ def read_vmec_output(cls, fname):
         return vmec_data
 
     @classmethod
-    def write_vmec_input(cls, eq, fname, header="", **kwargs):  # noqa: C901
+    def write_vmec_input(cls, eq, fname, header=None, **kwargs):  # noqa: C901
         """Write a VMEC input file for an equivalent DESC equilibrium.
 
         Parameters
@@ -1455,7 +1457,17 @@ def write_vmec_input(cls, eq, fname, header="", **kwargs):  # noqa: C901
         else:
             f = fname
         f.seek(0)
-
+        if header is None:
+            now = datetime.now()
+            date = now.strftime("%m/%d/%Y")
+            time = now.strftime("%H:%M:%S")
+            # auto header
+            header = (
+                " This VMEC input file was auto generated in DESC"
+                + f" version {desc.__version__} from a\n"
+                + "! DESC Equilibrium using the method VMECIO.write_vmec_input\n"
+                + "! on {} at {}.\n".format(date, time)
+            )
         f.write("! " + header + "\n")
         f.write("&INDATA\n")
 
@@ -1635,7 +1647,8 @@ def write_vmec_input(cls, eq, fname, header="", **kwargs):  # noqa: C901
                     + f"  ZBS({n:3.0f},{m:3.0f}) = {zbs:+14.8E}\n"
                 )
 
-        f.write("/")
+        f.write("/\n")
+        f.write("&END")
         f.close()
         return None