ENH: Change DSSP get_hbond_map to use capped_distance and PBC-aware distance calculations

package/AUTHORS

@@ -192,7 +192,7 @@ Chronological list of authors
   - Mingyi Xue
   - Meghan Osato
   - Anirvinya G
-  - Rishabh Shukla  
+  - Rishabh Shukla
   - Manish Kumar
   - Aditi Tripathi
   - Sukeerti T
@@ -247,24 +247,25 @@ Chronological list of authors
   - Jia-Xin Zhu
   - Tanish Yelgoe
 2025
-  - Joshua Raphael Uy 
+  - Joshua Raphael Uy
   - Namir Oues
-  - Pavel Buslaev  
+  - Pavel Buslaev
   - Lexi Xu
-  - BHM-Bob G  
+  - BHM-Bob G
   - Yu-Yuan (Stuart) Yang
   - James Rowe
-  - Debasish Mohanty  
+  - Debasish Mohanty
   - Abdulrahman Elbanna
   - Tulga-Erdene Sodjargal
   - Gareth Elliott
   - Marc Schuh
   - Sirsha Ganguly
   - Amruthesh Thirumalaiswamy
   - Ch Zhang
-  - Raúl Lois-Cuns  
+  - Raúl Lois-Cuns
   - Pranay Pelapkar
   - Shreejan Dolai
+  - Brady Johnston
 
 External code
 -------------

package/CHANGELOG

@@ -15,7 +15,7 @@ The rules for this file:
 
 -------------------------------------------------------------------------------
 ??/??/?? IAlibay, orbeckst, marinegor, tylerjereddy, ljwoods2, marinegor,
-         spyke7, talagayev
+         spyke7, talagayev, bradyajohnston
 
  * 2.11.0
 
@@ -30,6 +30,8 @@ Fixes
    DSSP by porting upstream PyDSSP 0.9.1 fix (Issue #4913)
 
 Enhancements
+ * Change `get_hbond_map` to use `distance_capped` to speedup finding H bonding pairs
+   and also take into account the periodic boundaries (PR #5182)
  * Enables parallelization for analysis.diffusionmap.DistanceMatrix
    (Issue #4679, PR #4745)
 

package/MDAnalysis/analysis/dssp/dssp.py

@@ -399,7 +399,11 @@ def _get_coords(self) -> np.ndarray:
 
     def _single_frame(self):
         coords = self._get_coords()
-        dssp = assign(coords, donor_mask=self._donor_mask)
+        dssp = assign(
+            coords,
+            donor_mask=self._donor_mask,
+            box=self._trajectory.ts.dimensions,
+        )
         self.results.dssp_ndarray.append(dssp)
 
     def _conclude(self):

package/MDAnalysis/analysis/dssp/pydssp_numpy.py

@@ -11,10 +11,13 @@
 
 import numpy as np
 
+from MDAnalysis.lib.distances import capped_distance
+
 CONST_Q1Q2 = 0.084
 CONST_F = 332
 DEFAULT_CUTOFF = -0.5
 DEFAULT_MARGIN = 1.0
+HBOND_SEARCH_CUTOFF = 5.0
 
 
 def _upsample(a: np.ndarray, window: int) -> np.ndarray:
@@ -118,10 +121,11 @@ def _get_hydrogen_atom_position(coord: np.ndarray) -> np.ndarray:
 
 def get_hbond_map(
     coord: np.ndarray,
-    donor_mask: np.ndarray = None,
+    donor_mask: np.ndarray | None = None,
     cutoff: float = DEFAULT_CUTOFF,
     margin: float = DEFAULT_MARGIN,
     return_e: bool = False,
+    box: np.ndarray | None = None,
 ) -> np.ndarray:
     """Returns hydrogen bond map
 
@@ -145,6 +149,14 @@ def get_hbond_map(
     return_e : bool, optional
         if to return energy instead of hbond map, by default False
 
+    box : array_like, optional
+        The unitcell dimensions of the system, which can be orthogonal or
+        triclinic and must be provided in the same format as returned by
+        :attr:`MDAnalysis.coordinates.timestep.Timestep.dimensions`:
+        ``[lx, ly, lz, alpha, beta, gamma]``.
+
+         .. versionadded:: 2.11.0
+
     Returns
     -------
     np.ndarray
@@ -156,6 +168,8 @@ def get_hbond_map(
     .. versionchanged:: 2.10.0
        Support masking of hydrogen donors via `donor_mask` (especially needed
        for ignoring HN on proline residues). Backport of PRO fix from pydssp 0.9.1.
+    .. versionchanged:: 2.11.0
+       Speedup with KDTree and support periodic boundary checking via `box` param.
     """
     n_residues, n_atom_types, _xyz = coord.shape
     assert n_atom_types in (
@@ -176,58 +190,59 @@ def get_hbond_map(
     # h.shape == (n_residues, 3)
     # coord.shape == (n_residues, 4, 3)
 
-    # distance matrix
-    n_1, c_0, o_0 = coord[1:, 0], coord[0:-1, 2], coord[0:-1, 3]
+    n_atoms, c_atoms, o_atoms = coord[1:, 0], coord[:-1, 2], coord[:-1, 3]
+
+    # We can reduce the need for a complete pairwise distance matrix by first searching for
+    # candidate pairs within a certain distance cutoff and only computing the energy
+    # for these relevant pairs rather than "potential" HBonds between far apart residues
+    pairs = capped_distance(
+        n_atoms,
+        o_atoms,
+        max_cutoff=HBOND_SEARCH_CUTOFF,
+        return_distances=False,
+        box=box,
+    )
+
+    # Exclude local pairs (i, i), (i, i+1), (i, i+2) that are too close for SS HBonds
+    pairs = pairs[abs(pairs[:, 0] - pairs[:, 1]) >= 2]
 
-    n = n_residues - 1
-    cmap = np.tile(c_0, (n, 1, 1))
-    omap = np.tile(o_0, (n, 1, 1))
-    nmap = np.tile(n_1, (1, 1, n)).reshape(n, n, 3)
-    hmap = np.tile(h_1, (1, 1, n)).reshape(n, n, 3)
+    # Exclude donor H absence (Proline)
+    if donor_mask is not None:
+        donor_indices = np.where(np.array(donor_mask) == 0)[0]
+        mask = ~np.isin(pairs[:, 0], donor_indices - 1)
+        pairs = pairs[mask]
 
-    d_on = np.linalg.norm(omap - nmap, axis=-1)
-    d_ch = np.linalg.norm(cmap - hmap, axis=-1)
-    d_oh = np.linalg.norm(omap - hmap, axis=-1)
-    d_cn = np.linalg.norm(cmap - nmap, axis=-1)
+    # compute distances and energy as previously but only for the potential pairs
+    # still returning the same energy matrix that would have otherwise been made
+    o_indices = pairs[:, 1]
+    n_indices = pairs[:, 0]
+    d_on = np.linalg.norm(o_atoms[o_indices] - n_atoms[n_indices], axis=-1)
+    d_ch = np.linalg.norm(c_atoms[o_indices] - h_1[n_indices], axis=-1)
+    d_oh = np.linalg.norm(o_atoms[o_indices] - h_1[n_indices], axis=-1)
+    d_cn = np.linalg.norm(c_atoms[o_indices] - n_atoms[n_indices], axis=-1)
 
     # electrostatic interaction energy
     # e[i, j] = e(CO_i) - e(NH_j)
-    e = np.pad(
+    e = np.zeros((n_residues, n_residues))
+    e[n_indices + 1, o_indices] = (
         CONST_Q1Q2
         * (1.0 / d_on + 1.0 / d_ch - 1.0 / d_oh - 1.0 / d_cn)
-        * CONST_F,
-        [[1, 0], [0, 1]],
+        * CONST_F
     )
 
     if return_e:  # pragma: no cover
         return e
 
-    # mask for local pairs (i,i), (i,i+1), (i,i+2)
-    local_mask = ~np.eye(n_residues, dtype=bool)
-    local_mask *= ~np.diag(np.ones(n_residues - 1, dtype=bool), k=-1)
-    local_mask *= ~np.diag(np.ones(n_residues - 2, dtype=bool), k=-2)
-    # mask for donor H absence (Proline)
-    donor_mask = (
-        np.array(donor_mask).astype(float)
-        if donor_mask is not None
-        else np.ones(n_residues, dtype=float)
-    )
-    donor_mask = np.tile(donor_mask[:, np.newaxis], (1, n_residues))
-    # hydrogen bond map (continuous value extension of original definition)
     hbond_map = np.clip(cutoff - margin - e, a_min=-margin, a_max=margin)
     hbond_map = (np.sin(hbond_map / margin * np.pi / 2) + 1.0) / 2
 
-    assert hbond_map.shape == local_mask.shape == donor_mask.shape
-
-    hbond_map *= local_mask
-    hbond_map *= donor_mask
-
     return hbond_map
 
 
 def assign(
     coord: np.ndarray,
-    donor_mask: np.ndarray = None,
+    donor_mask: np.ndarray | None = None,
+    box: np.ndarray | None = None,
 ) -> np.ndarray:
     """Assigns secondary structure for a given coordinate array,
     either with or without assigned hydrogens
@@ -240,12 +255,20 @@ def assign(
         (N, CA, C, O) atoms coordinates (if k=4), or (N, CA, C, O, H) coordinates
         (when k=5).
 
-    donor_mask : np.array
+    donor_mask : np.array | None, optional
          Mask out any hydrogens that should not be considered (in particular HN
          in PRO). If ``None`` then all H will be used (behavior up to 2.9.0).
 
          .. versionadded:: 2.10.0
 
+    box : array_like, optional
+        The unitcell dimensions of the system, which can be orthogonal or
+        triclinic and must be provided in the same format as returned by
+        :attr:`MDAnalysis.coordinates.timestep.Timestep.dimensions`:
+        ``[lx, ly, lz, alpha, beta, gamma]``.
+
+        .. versionadded:: 2.11.0
+
     Returns
     -------
     np.ndarray
@@ -257,6 +280,8 @@ def assign(
 
     .. versionchanged:: 2.10.0
        Support masking of donors.
+    .. versionchanged:: 2.11.0
+       Speedup with KDTree and support periodic boundary checking via `box` param.
 
     """
     # get hydrogen bond map

testsuite/MDAnalysisTests/analysis/test_dssp.py

@@ -1,8 +1,9 @@
 import glob
 
 import MDAnalysis as mda
+import numpy as np
 import pytest
-from MDAnalysis.analysis.dssp import DSSP, translate
+from MDAnalysis.analysis.dssp import DSSP, assign, translate
 
 from MDAnalysisTests.datafiles import DSSP as DSSP_FOLDER
 from MDAnalysisTests.datafiles import TPR, XTC
@@ -35,6 +36,19 @@ def test_trajectory(client_DSSP):
     )
 
 
+# ensure that we get different assigned results when using and not using the
+# donor mask which filters out prolines from being potential HBond donors as they
+# are missing hydrogens
+def test_donor_mask(client_DSSP):
+    u = mda.Universe(TPR, XTC).select_atoms("protein").universe
+    dssp = DSSP(u)
+    coords = dssp._get_coords()
+
+    assert not np.array_equal(
+        assign(coords), assign(coords, donor_mask=dssp._donor_mask)
+    )
+
+
 def test_atomgroup(client_DSSP):
     protein = mda.Universe(TPR, XTC).select_atoms("protein")
     run = DSSP(protein).run(**client_DSSP, stop=10)