# Recording Data¶

## Overview¶

Several types of data can be recorded using GPU-accelerated methods in DASH, including energies on an aggregate or fine-grained bases, temperature, kinetic energy, pressture, virial coefficients, volume, and simulation boundaries. Other data types can be recorded via Python Operation with minimal performance overhead.

## Recording data¶

The dataManager member of State handles data recording. To record temperature of all atoms, for instance, one would write

#record temperature every 100 turns
temperatureData = state.dataManager.recordTemperature(interval=100)

integrater.run(10000)

#print python list of recorded temperatures
print temperature.vals
#print python list of turns on which these values were recorded
print temperature.turns

and as shown, access the recorded values through the vals member and the turns on which they were recorded through the turns member. This structure is used for recording all data types.

Details on recording specific data types is given below.

## Recording energies and group-group energies¶

Example

ljcut = FixLJCut(state, 'ljcut')
ewald = FixChargeEwald(state, 'chargeEwald', 'all')
def giveNextTurn(currentTurn):
if currentTurn==0:
return 1
else:
return currentTurn*2

#this will record the potential energy of all atoms every 100 turns
engDataSimple = state.dataManager.recordEnergy(handle='all', mode='scalar', interval=100)

#this will record per-particle energies (as denoted by the mode)
#every turn as given by the giveNextTurn function.  It will only
#record contributions due to ljcut and ewald fixes.  Any fix
#can be given in the fixes list.
engDataLogSpacing = state.dataManager.recordEnergy(handle='all', mode='vector', collectGenerator=giveNextTurn, fixes=[ljcut, ewald])

#computes LJ interactions between groupA and groupB
engDataGroupGroup = state.dataManager.recordEnergy(handle='groupA', handleB='groupB', mode='scalar', interval=100, fixes=[ljcut])

verlet = IntergatorVerlet(state)

verlet.run(10000)

#prints list of per-particle energy lists
print engDataLogSpacing.vals

Arguments

handle: Group handle for which energies will be compted. Defaults to 'all'.

mode: 'scalar' or 'vector'. 'scalar' computes the sum of relevant energies while 'vector' computes per-particle energies represented as a python list. Defaults to 'scalar'

interval: How often data is recorded. Either interval or collectGenerator must be specified

collectGenerator: Function which takes the current turn on which data is being recorded and returns the next turn on which it should be recorded. Either interval or collectGenerator must be specified

fixes: Fixes for which energy will be recorded. Defaults to all active fixes

handleB: For group-group energies, the handle of the other group. This is the other parameter which must be specified to perform group-group energy calculations.

## Recording temperatures and kinetic energies¶

ljcut = FixLJCut(state, 'ljcut')
ewald = FixChargeEwald(state, 'chargeEwald', 'all')

#this will record the temperature of all atoms every 100 turns
tempDataScalar = state.dataManager.recordTemperature(handle='all', mode='scalar', interval=100)

#this will record per-particle kinetic energies (as denoted by the mode)
#every turn as given by the giveNextTurn function.
tempDataVector = state.dataManager.recordEnergy(handle='all', mode='vector', interval=100)

verlet = IntergatorVerlet(state)

verlet.run(10000)

#prints list of tenoeratures followed by the turns at which those
#data points were recorded
print tempDataScalar.vals, tempDataScalar.turns

Arguments

handle: Group handle for which temperature will be compted. Defaults to 'all'.

mode: 'scalar' or 'vector'. 'scalar' computes the temperature of the group given by handle while 'vector' computes per-particle kinetic energies represented as a python list. Defaults to 'scalar'

interval: How often data is recorded. Either interval or collectGenerator must be specified

collectGenerator: Function which takes the current turn on which data is being recorded and returns the next turn on which it should be recorded. Either interval or collectGenerator must be specified

## Recording pressures and virial coefficients¶

#this will record the system's pressure every 100 turns
pressureData = state.dataManager.recordPressure(handle='all', mode='scalar', interval=100)

#records pressure tensor
pressureDataTensor = state.dataManager.recordPressure(handle='all', mode='tensor', interval=100)

verlet = IntergatorVerlet(state)

verlet.run(10000)

#prints list of pressures
print pressureData.vals

Arguments

handle: Group handle for which temperature will be compted. Defaults to 'all'.

mode: 'scalar' or 'tensor'. 'scalar' computes the pressure of the group given by handle while 'tensor' computes pressuretensor due to that group. Defaults to 'scalar'

interval: How often data is recorded. Either interval or collectGenerator must be specified

collectGenerator: Function which takes the current turn on which data is being recorded and returns the next turn on which it should be recorded. Either interval or collectGenerator must be specified

## Recording volume and boundaries¶

The system bounding box can also be recorded. From this volume, side lens, rates of volume change, etc, can easily be computed.

#this will record the system's pressure every 100 turns
boundsData = state.dataManager.recordBounds(interval=100)

verlet = IntergatorVerlet(state)

verlet.run(10000)

#prints list of pressures
volumes = []
xSideLengths = []
for bounds in boundsData.vals:
volumes.append(bounds.volume())
xSideLengths.append(bounds.hi[0] - bounds.lo[0])

#all the volumes computed
print volumes

Arguments

interval: How often data is recorded. Either interval or collectGenerator must be specified

collectGenerator: Function which takes the current turn on which data is being recorded and returns the next turn on which it should be recorded. Either interval or collectGenerator must be specified

## Turning off recording¶

Recording of a data set can be stopped at any time by calling the stopRecord method of the DataManager

myDataSet = state.dataManager.recordTemperature(handle='all', mode='scalar', interval=100)

#turns off recording
state.dataManager.stopRecord(myDataSet)