Add neopdf PDF interpolation backend

.github/actions/install_conda_pip/action.yml

@@ -27,7 +27,7 @@ inputs:
   nnpdf-extras:
     required: true
     description: "Which extras to install"
-    default: "[qed,tests,hyperopt]"
+    default: "[qed,tests,hyperopt,neopdf]"
 
 
 runs:
@@ -44,3 +44,4 @@ runs:
       shell: bash -l {0}
       run: |
         pip install -e .${{ inputs.nnpdf-extras }}
+    - uses: ./.github/actions/set_neopdf_datapath

.github/actions/set_neopdf_datapath/action.yml

@@ -0,0 +1,12 @@
+name: Set NEOPDF_DATA_PATH
+
+# Point NeoPDF at the directory where lhapdf-management stores PDF sets,
+# so it reads local files instead of downloading from the LHAPDF servers.
+
+runs:
+  using: "composite"
+  steps:
+    - name: Point NeoPDF at the LHAPDF data directory
+      shell: bash -l {0}
+      run: |
+        echo "NEOPDF_DATA_PATH=$(python -c 'from lhapdf_management.configuration import environment; print(environment.datapath)')" >> $GITHUB_ENV

.github/workflows/all_tests_nnpdf.yml

@@ -114,6 +114,7 @@ jobs:
     runs-on: ubuntu-latest
     env:
       KERAS_BACKEND: torch
+      NNPDF_PDF_BACKEND: neopdf
     steps:
     - uses: actions/checkout@v6
     - uses: actions/setup-python@v5
@@ -129,9 +130,10 @@ jobs:
         # at import on CPU-only Linux + CPython 3.13. Pinning torch<2.12 also
         # pins triton to 3.6.x. Remove this pin once the upstream issue is
         # resolved (see https://github.com/nascheme/triton/issues/43).
-        pip install ".[nolha,torch]" "torch<2.12"
+        pip install ".[neopdf,torch]" "torch<2.12"
         # Since there is no LHAPDF in the system, initialize the folder and download pdfsets.index
         lhapdf-management update --init
+    - uses: ./.github/actions/set_neopdf_datapath
     - name: Test we can run one runcard
       shell: bash -l {0}
       run: |
@@ -151,6 +153,7 @@ jobs:
     runs-on: ubuntu-latest
     env:
       KERAS_BACKEND: jax
+      NNPDF_PDF_BACKEND: neopdf
     steps:
     - uses: actions/checkout@v6
     - uses: actions/setup-python@v5
@@ -159,9 +162,10 @@ jobs:
     - name: Install nnpdf without LHAPDF
       shell: bash -l {0}
       run: |
-        pip install .[nolha,jax]
+        pip install .[neopdf,jax]
         # Since there is no LHAPDF in the system, initialize the folder and download pdfsets.index
         lhapdf-management update --init
+    - uses: ./.github/actions/set_neopdf_datapath
     - name: Test we can run one runcard
       shell: bash -l {0}
       run: |

pyproject.toml

@@ -98,6 +98,8 @@ fiatlux = {version = "*", optional = true}
 # without lhapdf
 pdfflow = {version = "^1.2.1", optional = true}
 lhapdf-management = {version = "^0.6", optional = true}
+# neopdf interpolation backend
+neopdf-hep = {version = "^0.3", optional = true}
 # torch
 torch = {version = "*", optional = true}
 # jax
@@ -110,7 +112,9 @@ pymongo = {version = "<4", optional = true}
 tests = ["pytest", "pytest-mpl", "hypothesis", "pytest-cov"]
 docs = ["sphinxcontrib-bibtex", "sphinx-rtd-theme", "sphinx", "tabulate"]
 qed = ["fiatlux"]
-nolha = ["pdfflow", "lhapdf-management"]
+pdfflow = ["pdfflow", "lhapdf-management"]
+neopdf = ["neopdf-hep", "lhapdf-management"]
+nolha = ["neopdf-hep", "lhapdf-management"]
 torch = ["torch"]
 jax = ["jax"]
 hyperopt = ["hyperopt", "setuptools"]

validphys2/src/validphys/lhapdf_compatibility.py

@@ -1,13 +1,18 @@
 """
-    Module for LHAPDF compatibility backends
+Module for LHAPDF compatibility backends
 
-    If LHAPDF is installed, the module will transparently hand over everything to LHAPDF
-    if LHAPDF is not available, it will try to use a combination of the packages
-        `lhapdf-management` and `pdfflow`
-    which cover all the features of LHAPDF used during the fit (and likely most of validphys)
+If LHAPDF is installed, the module will transparently hand over everything to LHAPDF.
+If LHAPDF is not available, it will try to use a combination of the packages
+    `lhapdf-management` and `pdfflow`
+which cover all the features of LHAPDF used during the fit (and likely most of validphys).
+
+The NeoPDF interpolation library can be selected by setting ``pdf_backend: neopdf``
+in the NNPDF profile (``nnprofile.yaml``), or via the ``NNPDF_PDF_BACKEND`` environment
+variable which takes precedence over the profile.
 """
 
 from functools import cached_property
+import os
 
 import numpy as np
 
@@ -25,17 +30,44 @@
 
     USING_LHAPDF = False
 
+_BACKEND_ENV_VAR = "NNPDF_PDF_BACKEND"
+_VALID_BACKENDS = ("lhapdf", "pdfflow", "neopdf")
+
+
+class InvalidPDFBackend(Exception):
+    pass
+
+
+def _active_backend():
+    """Return the active PDF backend.
+
+    Resolution order (highest priority first):
+    1. ``NNPDF_PDF_BACKEND`` environment variable
+    2. ``pdf_backend`` key in the NNPDF profile (``nnprofile.yaml``)
+    """
+    backend = os.environ.get(_BACKEND_ENV_VAR)
+    if backend is None:
+        try:
+            from nnpdf_data.utils import get_nnpdf_profile
+
+            backend = get_nnpdf_profile().get("pdf_backend", "lhapdf")
+        except Exception:
+            backend = "lhapdf"
+    return backend.lower()
+
 
 class _PDFFlowPDF:
     """Wrapper around the PDFFlow PDF so that it can be used as an LHAPDF
     set by validphys
     Takes as input a pdf_meta object (which is a PDFset from lhapdf_management
     and which knows where the PDF needs to be loaded from) and a single member
 
-    Loading the PDF is done in a lazy manner since most of the time only a few members are needed.
+    Loading the PDF is done in a lazy manner since most of the time only a few
+    members are needed.
 
-    Since PDFFlow is only utilized to load the PDF for interpolation, the import is delayed until
-    the first call to `mkPDF`. This allows the usage of most of validphys without tensorflow.
+    Since PDFFlow is only utilized to load the PDF for interpolation, the import
+    is delayed until the first call to `mkPDF`. This allows the usage of most of
+    validphys without tensorflow.
     """
 
     def __init__(self, pdf_meta, member):
@@ -96,13 +128,54 @@ def xfxQ2(self, a, b, c=None):
         return self.xfxQ(a, b, np.sqrt(c))
 
 
+class _NeoPDFPDF:
+    """Thin wrapper around a single NeoPDF member exposing the LHAPDF-compatible interface."""
+
+    def __init__(self, neo_member):
+        self._member = neo_member
+        self._pids = neo_member.pids()
+
+    def flavors(self):
+        return self._pids
+
+    def _xfxQ_all_pid(self, x, q):
+        scalar_input = np.ndim(x) == 0 and np.ndim(q) == 0
+        x = np.atleast_1d(x)
+        q = np.atleast_1d(q)
+        vals = np.array(
+            [
+                self._member.xfxQ2_allpids(self._pids, float(xi), float(qi) ** 2)
+                for xi, qi in zip(x, q)
+            ]
+        )  # (n_points, n_pids)
+        if scalar_input:
+            return dict(zip(self._pids, vals[0]))
+        return dict(zip(self._pids, vals.T))
+
+    def xfxQ(self, a, b, c=None):
+        if c is None:
+            return self._xfxQ_all_pid(a, b)
+        ret_dict = self.xfxQ(b, c)
+        zeros = np.zeros_like(b)
+        if isinstance(a, int):
+            return ret_dict.get(a, zeros)
+        return np.array([ret_dict.get(i, zeros) for i in a]).T
+
+    def xfxQ2(self, a, b, c=None):
+        if c is None:
+            return self.xfxQ(a, np.sqrt(b))
+        return self.xfxQ(a, b, np.sqrt(c))
+
+
 def make_pdf(pdf_name, member=None):
-    """Load a PDF
-    if member is given, load the single member otherwise, load the entire set as a list
+    """Load a single member if specified, otherwise load the entire set as a list.
 
-    if LHAPDF is provided, it returns LHAPDF PDF instances
-    otherwise it returns and object which is _compatible_ with LHAPDF
-    for lhapdf functions for the selected backend
+    If LHAPDF is provided, it returns LHAPDF PDF instances otherwise it returns and
+    object which is _compatible_ with LHAPDF for lhapdf functions for the selected
+    backend.
+
+    The backend can be overridden by setting the ``NNPDF_PDF_BACKEND`` environment
+    variable to ``neopdf`` to use the NeoPDF interpolation library.
 
     Parameters:
     -----------
@@ -115,11 +188,25 @@ def make_pdf(pdf_name, member=None):
     --------
         list(pdf_sets)
     """
-    if USING_LHAPDF:
+    backend = _active_backend()
+
+    if backend not in _VALID_BACKENDS:
+        raise InvalidPDFBackend(f"Unknown backend {backend!r}. Options are: {_VALID_BACKENDS}")
+
+    if backend == "lhapdf":
         if member is None:
             return lhapdf.mkPDFs(pdf_name)
         return [lhapdf.mkPDF(pdf_name, member)]
 
+    if backend == "neopdf":
+        from neopdf.pdf import PDF as _NeoPDF
+
+        members = _NeoPDF.mkPDFs(pdf_name)
+        if member is None:
+            return [_NeoPDFPDF(m) for m in members]
+        return [_NeoPDFPDF(members[member])]
+
+    # backend == "pdfflow"
     pdf_meta = lhapdf.load_pdf_meta(pdf_name)
     if member is None:
         return [_PDFFlowPDF(pdf_meta, m) for m in range(len(pdf_meta))]

validphys2/src/validphys/nnprofile_default.yaml

@@ -67,6 +67,9 @@ photon_qed_urls:
 
 photon_qed_index: 'photondata.json'
 
+# PDF interpolation backend: "lhapdf" (default), "pdfflow", or "neopdf"
+pdf_backend: lhapdf
+
 lhapdf_urls:
     - 'http://lhapdfsets.web.cern.ch/lhapdfsets/current/'
 nnpdf_pdfs_urls: