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Add pbc kwarg to Contacts #2646

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Apr 22, 2020
Merged

Add pbc kwarg to Contacts #2646

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921eb56
Fixes #2368: added option to calculate distances using PBC
ss62171 Mar 25, 2020
d796742
Added test to check distance calculated using PBC
ss62171 Mar 25, 2020
856344c
test added
ss62171 Mar 29, 2020
05a442c
documented changes
ss62171 Mar 29, 2020
c97cacc
added box_dim and test modified
ss62171 Mar 31, 2020
8b204d2
added lambda func to get dimension of box
ss62171 Mar 31, 2020
ee62918
edit changelog and docstring of class
ss62171 Apr 8, 2020
043819b
fixed typo
ss62171 Apr 9, 2020
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24 changes: 19 additions & 5 deletions package/MDAnalysis/analysis/contacts.py
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Original file line number Diff line number Diff line change
Expand Up @@ -424,18 +424,28 @@ def __init__(self, u, select, refgroup, method="hard_cut", radius=4.5,
self.select = select
self.grA = u.select_atoms(select[0])
self.grB = u.select_atoms(select[1])

self.is_box = self.fraction_kwargs.get('is_box')
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The name is_box isn't particularly intuitive; something like pbc would be better.

Also, since it is only used in __init__ and not in the fraction_contacts methods where fraction_kwargs is passed, it'd make more sense to directly include as an argument of __init__ rather than through kwargs. This would also make it easier to include in the docs here.


# contacts formed in reference
self.r0 = []
self.initial_contacts = []

if isinstance(refgroup[0], AtomGroup):
refA, refB = refgroup
self.r0.append(distance_array(refA.positions, refB.positions))
if(self.is_box):
self.r0.append(distance_array(refA.positions, refB.positions,
box=refA.universe.dimensions))
else:
self.r0.append(distance_array(refA.positions, refB.positions))
self.initial_contacts.append(contact_matrix(self.r0[-1], radius))
else:
for refA, refB in refgroup:
self.r0.append(distance_array(refA.positions, refB.positions))
if(self.is_box):
self.r0.append(distance_array(refA.positions, refB.positions,
box=refA.universe.dimensions))
else:
self.r0.append(distance_array(refA.positions, refB.positions))

self.initial_contacts.append(contact_matrix(self.r0[-1],
radius))

Expand All @@ -444,9 +454,13 @@ def _prepare(self):

def _single_frame(self):
self.timeseries[self._frame_index][0] = self._ts.frame

# compute distance array for a frame
d = distance_array(self.grA.positions, self.grB.positions)
if(self.is_box):
d = distance_array(self.grA.positions, self.grB.positions,
self._ts.dimensions)
else:
d = distance_array(self.grA.positions, self.grB.positions)

for i, (initial_contacts, r0) in enumerate(zip(self.initial_contacts,
self.r0), 1):
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25 changes: 25 additions & 0 deletions testsuite/MDAnalysisTests/analysis/test_contacts.py
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Expand Up @@ -37,6 +37,8 @@
from MDAnalysisTests.datafiles import (
PSF,
DCD,
TPR,
XTC,
contacts_villin_folded,
contacts_villin_unfolded,
contacts_file
Expand Down Expand Up @@ -302,6 +304,29 @@ def test_non_callable_method(self, universe):
with pytest.raises(ValueError):
self._run_Contacts(universe, method=2, stop=2)

def test_distance_box(self):
u = mda.Universe(TPR, XTC)
sel1 = "(resname ARG LYS) and (name NH* NZ)"
sel2 = "(resname ASP GLU) and (name OE* OD*)"
acidic = u.select_atoms(sel2)
basic = u.select_atoms(sel1)
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You could focus the test on a particular pair we know is split across the periodic boundary, to make it easier to directly check the distances measured are what we expect given PBC.


q = contacts.Contacts(u,
select=(sel1, sel2),
refgroup=(acidic, basic),
method="hard_cut",
kwargs={'is_box': True})

r = contacts.Contacts(u,
select=(sel1, sel2),
refgroup=(acidic, basic),
method="hard_cut")

q.r0 = np.array(q.r0).squeeze()
r.r0 = np.array(r.r0).squeeze()
assert_array_equal(q.r0,r.r0)
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We expect the distance to be different with or without consideration of the periodic boundaries, so this test is currently failing; maybe you could compare directly with what we expect the values to be instead?




def test_q1q2():
u = mda.Universe(PSF, DCD)
Expand Down