vmc.hist line number
vmc.hist line number
I noticed that the number of vmc.hist files that is given by reblock utility is different from the number of VMC steps given in the input. For example, I decided to make 5 000 000 VMC steps, and reblock says there are 312500 lines in vmc.hist. Even dividing over the decorrelation steps (12), it is still too less. What is the reason?
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Mike Towler
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Re: vmc.hist line number
It's basically parallel stuff - are you running on 16 processors by any chance? To quote the output of 'casinohelp vmc_nstep':
CASINO HELP SYSTEM
==================
Keyword : vmc_nstep
Title : Number of (main) VMC steps
Type : Integer
Level : Basic
DESCRIPTION
-----------
Total number of VMC steps summed over all processors; this corresponds to
the total number of particle configurations for which the energy (and other
quantities to be averaged) are calculated.
Note that because adjacent moves are likely to be serially correlated, there
is also an inner decorrelation loop of length VMC_DECORR_PERIOD, so the total
number of configuration moves attempted in a VMC run following equilibration
is VMC_NSTEP*VMC_DECORR_PERIOD.
On parallel machines, each core will do the same number of steps and for
each step the energy is averaged over the cores and written to the vmc.hist
file (which will ultimately contain VMC_NSTEP/NCORES lines - though
VMC_AVE_PERIOD adjacent lines may be averaged over to reduce the file size).
This means that if VMC_NSTEP is not divisible by the number of cores then it
will internally be rounded up to the nearest multiple of the number of cores
(example: on a 12-core machine, given VMC_NSTEP=20 in input, CASINO will
round up VMC_NSTEP to 24; each core will then do two steps and a total of two
records will be written to vmc.hist, each of which is an average of 12
energies). On a single-core machine with VMC_NSTEP=20, CASINO will move the
single config 20 times, and 20 records will be written to vmc.hist.
Note the VMC_NBLOCK keyword may be used to vary the frequency with which
checkpointing is done i.e. how often we write the data to disk; it does not
affect the total number of VMC steps and expectation values such as average
energy should be independent of it.
CASINO HELP SYSTEM
==================
Keyword : vmc_nstep
Title : Number of (main) VMC steps
Type : Integer
Level : Basic
DESCRIPTION
-----------
Total number of VMC steps summed over all processors; this corresponds to
the total number of particle configurations for which the energy (and other
quantities to be averaged) are calculated.
Note that because adjacent moves are likely to be serially correlated, there
is also an inner decorrelation loop of length VMC_DECORR_PERIOD, so the total
number of configuration moves attempted in a VMC run following equilibration
is VMC_NSTEP*VMC_DECORR_PERIOD.
On parallel machines, each core will do the same number of steps and for
each step the energy is averaged over the cores and written to the vmc.hist
file (which will ultimately contain VMC_NSTEP/NCORES lines - though
VMC_AVE_PERIOD adjacent lines may be averaged over to reduce the file size).
This means that if VMC_NSTEP is not divisible by the number of cores then it
will internally be rounded up to the nearest multiple of the number of cores
(example: on a 12-core machine, given VMC_NSTEP=20 in input, CASINO will
round up VMC_NSTEP to 24; each core will then do two steps and a total of two
records will be written to vmc.hist, each of which is an average of 12
energies). On a single-core machine with VMC_NSTEP=20, CASINO will move the
single config 20 times, and 20 records will be written to vmc.hist.
Note the VMC_NBLOCK keyword may be used to vary the frequency with which
checkpointing is done i.e. how often we write the data to disk; it does not
affect the total number of VMC steps and expectation values such as average
energy should be independent of it.
Re: vmc.hist line number
Thank You, 16 processors indeed.