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#!/usr/bin/env python3
# encoding: utf-8
"""
_FixedStep.py
Created by Graham Dennis on 2008-03-01.
Copyright (c) 2008-2012, Graham Dennis
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
"""
from xpdeint.Segments.Integrators.Integrator import Integrator
from xpdeint.Utilities import lazy_property
class _FixedStep (Integrator):
# Is this integrator capable of doing cross-propagation integration?
isCrossCapable = False
def __init__(self, *args, **KWs):
Integrator.__init__(self, *args, **KWs)
# Set default variables
self._cross = False
# Is this integrator being used as a cross-propagation integrator?
self.cross = KWs.get('cross', False)
def _getCross(self):
return self._cross
def _setCross(self, value):
if value and not self.stepper.isCrossCapable:
raise AssertionError("This stepper (%s) does not support cross-propagation." % str(type(self.stepper)))
else:
self._cross = value
cross = property(_getCross, _setCross)
del _getCross, _setCross
@lazy_property
def bannedFeatures(self):
"""Return the features which are not permitted to be inserted by this instance."""
# If we are cross-propagating, then ErrorCheck cannot simply subdivide the step.
# And we don't want to sample anything for moment groups
# GD: The reason that we disable auto-vectorisation is subtle, and I don't completely
# understand it myself. But after much fiddling, it seems that the last step in the
# integrator where the results from the integration step are copied back into the main
# array does not sync with the last memory write in the step (as the last step with the
# auto-vectorisation feature would have been to a real*, so come time for the copy to
# a complex variable, the CPU/compiler sees fit to reorder the stores causing all hell
# to break loose). This isn't a particularly good explanation, but my understanding of
# this isn't particularly strong.
#
# My evidence is that everything works fine if I turn off auto-vectorisation, and it also
# works fine if I have it on but have a printf before (but not after) the copy operation
# (inside the loop) to force a read from the memory that is going to be written to and so force
# the correct ordering between the two writes. It may be possible to turn on the
# auto-vectorisation feature if a memory barrier is added before the final copy step, but I
# don't know how to implement a cross-platform memory barrier, and I'm not about to find out.
if self.cross:
return ['ErrorCheck', 'Output', 'AutoVectorise']
else:
return None
@lazy_property
def step(self):
return ''.join([str(self.interval), '/(real)', str(self.stepCount)])
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