From 9dcf621618fe76281a486af7bfba364e7bd26c13 Mon Sep 17 00:00:00 2001
From: Rob Moss <robm.dev@gmail.com>
Date: Wed, 27 Oct 2021 13:54:05 +1100
Subject: [PATCH] Fix a bug in pypfilt.state.earlier_states
This bug was introduced in commit 408b5f1 but was not initially detected
due to stale tox artefacts.
---
src/pypfilt/state.py | 11 ++++++---
tests/test_earlier_state.py | 47 +++++++++++++++++++++++++++++++++++++
2 files changed, 55 insertions(+), 3 deletions(-)
create mode 100644 tests/test_earlier_state.py
diff --git a/src/pypfilt/state.py b/src/pypfilt/state.py
index b22f0bf..abd240b 100644
--- a/src/pypfilt/state.py
+++ b/src/pypfilt/state.py
@@ -168,10 +168,15 @@ def earlier_states(hist, ix, steps):
"""
logger = logging.getLogger(__name__)
+ # Return the current particles when looking back zero time-steps.
+ if steps == 0:
+ logger.debug('Looking back zero steps')
+ return hist[ix - steps]
+
# Don't go too far back (negative indices jump into the future).
if steps > ix:
msg_fmt = 'Cannot look back {} time-steps, will look back {}'
- logger.warn(msg_fmt.format(steps, ix))
+ logger.debug(msg_fmt.format(steps, ix))
steps = min(steps, ix)
# Start with the parent indices for the current particles, which allow us
@@ -179,10 +184,10 @@ def earlier_states(hist, ix, steps):
parent_ixs = np.copy(hist['prev_ix'][ix])
# Continue looking back one time-step, and only update the parent indices
- # at time-step T if the particles were resampled at time-step T+1.
+ # if the particles were resampled.
for i in range(1, steps):
step_ix = ix - i
- if hist['resampled'][step_ix + 1, 0]:
+ if hist['resampled'][step_ix, 0]:
parent_ixs = hist['prev_ix'][step_ix, parent_ixs]
return hist[ix - steps, parent_ixs]
diff --git a/tests/test_earlier_state.py b/tests/test_earlier_state.py
new file mode 100644
index 0000000..327016b
--- /dev/null
+++ b/tests/test_earlier_state.py
@@ -0,0 +1,47 @@
+"""
+Test the behaviour of ``pypfilt.state.earlier_state()``.
+"""
+
+import numpy as np
+import pypfilt.state
+
+
+def test_earlier_state():
+ dtype = [('prev_ix', np.int_), ('resampled', np.bool_),
+ ('id', np.float_)]
+ num_steps = 6
+ num_px = 4
+ same_order = np.arange(num_px)
+ reverse_order = same_order[::-1]
+ hist = np.zeros(shape=(num_steps, num_px), dtype=dtype)
+
+ # No resampling, particles remain in the same order.
+ hist['prev_ix'][:, :] = same_order[None, :]
+ hist['id'][:, :] = same_order[None, :]
+
+ for ix in [1, 3, 5]:
+ for steps_back in [0, 1, 2, 3]:
+ prev_state = pypfilt.state.earlier_states(hist, ix, steps_back)
+ assert np.array_equal(prev_state['id'], same_order)
+
+ # Reverse the particle ordering at step 2.
+ resample_ix = 2
+ hist['resampled'][resample_ix, :] = True
+ hist['prev_ix'][resample_ix, :] = reverse_order
+ hist['id'][resample_ix:, :] = reverse_order[None, :]
+
+ # Starting at all time-steps prior to the resampling event, the particles
+ # should be returned in their original order.
+ for ix in range(resample_ix):
+ for steps_back in range(num_steps):
+ state = pypfilt.state.earlier_states(hist, ix, steps_back)
+ ids = state['id']
+ assert np.array_equal(ids, same_order)
+
+ # Starting at all time-steps from the resampling event, the particles
+ # should be returned in reverse order.
+ for ix in range(2, num_steps):
+ for steps_back in range(num_steps):
+ state = pypfilt.state.earlier_states(hist, ix, steps_back)
+ ids = state['id']
+ assert np.array_equal(ids, reverse_order)
--
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