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v_name = per-atom vector calculated by an atom-style variable with name :pre
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zero or more keyword/arg pairs may be appended :l
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keyword = {norm} or {units} or {file} or {ave} or {overwrite} or {title1} or {title2} or {title3} :l
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{units} arg = {box} or {lattice} or {reduced}
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keyword = {region} or {bound} or {discard} or {norm} or {ave} or {units} or {file} or {overwrite} or {title1} or {title2} or {title3} :l
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{region} arg = region-ID
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{bound} args = x/y/z lo hi
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x/y/z = {x} or {y} or {z} to bound bins in this dimension
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lo = {lower} or coordinate value (distance units)
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hi = {upper} or coordinate value (distance units)
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{discard} arg = {mixed} or {no} or {yes}
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mixed = discard atoms outside bins only if bin bounds are explicitly set
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no = always keep out-of-bounds atoms
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yes = always discard out-of-bounds atoms
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{norm} arg = {all} or {sample}
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{region} arg = region-ID
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region-ID = ID of region atoms must be in to contribute to spatial averaging
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{ave} args = {one} or {running} or {window M}
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one = output new average value every Nfreq steps
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running = output cumulative average of all previous Nfreq steps
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window M = output average of M most recent Nfreq steps
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{units} arg = {box} or {lattice} or {reduced}
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{file} arg = filename
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filename = file to write results to
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{overwrite} arg = none = overwrite output file with only latest output
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fix 1 all ave/spatial 10000 1 10000 z lower 0.02 c_myCentro units reduced &
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title1 "My output values"
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fix 1 flow ave/spatial 100 10 1000 y 0.0 1.0 vx vz norm sample file vel.profile
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fix 1 flow ave/spatial 100 5 1000 z lower 1.0 y 0.0 2.5 density/mass ave running :pre
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fix 1 flow ave/spatial 100 5 1000 z lower 1.0 y 0.0 2.5 density/mass ave running
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fix 1 flow ave/spatial 100 5 1000 z lower 1.0 y 0.0 2.5 density/mass bound y 5.0 20.0 discard yes ave running :pre
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The fix ave/spatial command has been replaced by the more flexible
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"fix ave/chunk"_fix_ave_chunk.html and "compute
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chunk/atom"_compute_chunk_atom.html commands. The fix ave/spatial
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command will be removed from LAMMPS sometime in the summer of 2015.
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Any fix ave/spatial command can be replaced by the two new commands.
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You simply need to split the fix ave/spatial arguments across the two
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new commands. For example, this command:
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fix 1 flow ave/spatial 100 10 1000 y 0.0 1.0 vx vz norm sample file vel.profile :pre
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compute cc1 flow chunk/atom bin/1d y 0.0 1.0
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fix 1 flow ave/chunk 100 10 1000 cc1 vx vz norm sample file vel.profile :pre
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Each per-atom property is also averaged over atoms in each bin. Bins
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can be 1d layers or slabs, 2d pencils, or 3d boxes. This depends on
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how many times (1, 2, or 3) the {dim}, {origin}, and {delta} settings
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are specified in the fix ave/spatial command. For 2d or 3d bins,
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there is no restriction on specifying dim = x before dim = y, or dim =
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y before dim = z. Bins in a particular {dim} have a bin size in that
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dimension given by {delta}. Every Nfreq steps, when averaging is
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Each per-atom property is also averaged over atoms in each bin. The
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way the averaging is one across the {Nrepeat} timesteps to produce
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output on the {Nfreq} timesteps, and across multiple {Nfreq} outputs,
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is determined by the {norm} and {av} keyword settings, as discussed
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Bins can be 1d layers or slabs, 2d pencils, or 3d boxes. This depends
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on how many times (1, 2, or 3) the {dim}, {origin}, and {delta}
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settings are specified in the fix ave/spatial command. For 2d or 3d
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bins, there is no restriction on specifying dim = x before dim = y, or
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dim = y before dim = z. Bins in a particular {dim} have a bin size in
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that dimension given by {delta}. Every Nfreq steps, when averaging is
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169
being performed and the per-atom property is calculated for the first
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170
time, the number of bins and the bin sizes and boundaries are
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computed. Thus if the simulation box changes size during a
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simulation, the number of bins and their boundaries may also change.
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In each dimension, bins are defined relative to a specified {origin},
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which may be the lower/upper edge of the simulation box (in {dim}) or
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its center point, or a specified coordinate value. Starting at the
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origin, sufficient bins are created in both directions to completely
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cover the box. On subsequent timesteps every atom is mapped to one of
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the bins. Atoms beyond the lowermost/uppermost bin in a dimension are
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counted in the first/last bin in that dimension.
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which may be the lower/upper edge of the simulation box in that
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dimension, or its center point, or a specified coordinate value.
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Starting at the origin, sufficient bins are created in both directions
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to completely span the bin extent in that dimension. By default the
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bin extent is the entire simulation box.
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The {bound} keyword can be used one or more times to limit the extent
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of bin coverage in specified dimensions, i.e. to only bin a portion of
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the box. If the {lo} setting is {lower} or the {hi} setting is
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{upper}, the bin extent in that direction extends to the box boundary.
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If a numeric value is used for {lo} and/or {hi}, then the bin extent
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in the {lo} or {hi} direction extends only to that value, which is
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assumed to be inside (or at least near) the simulation box boundaries,
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though LAMMPS does not check for this.
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On each sampling timestep, each atom is mapped to the bin it currently
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belongs to, based on its current position. Note that the group-ID and
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region keyword can exclude specific atoms from this operation, as
192
discussed above. Note that between reneighboring timesteps, atoms can
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move outside the current simulation box. If the box is periodic (in
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that dimension) the atom is remapping into the periodic box for
195
purposes of binning. If the box in not periodic, the atom may have
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moved outside the bounds of any bin.
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The {discard} keyword determines what is done with any atom which is
199
outside the bounds of any bin. If {discard} is set to {yes}, the atom
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will be ignored and not contribute to any bin averages. If {discard}
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is set to {no}, the atom will be counted as if it were in the first or
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last bin in that dimension. If (discard} is set to {mixed}, which is
203
the default, it will only be counted in the first or last bin if bins
204
extend to the box boundary in that dimension. This is the case if the
205
{bound} keyword settings are {lower} and {upper}, which is the
206
default. If the {bound} keyword settings are numeric values, then the
207
atom will be ignored if it is outside the bounds of any bin. Note
208
that in this case, it is possible that the first or last bin extends
209
beyond the numeric {bounds} settings, depending on the specified
210
{origin}. If this is the case, the atom is only ignored if it is
211
outside the first or last bin, not if it is simply outside the numeric
149
214
For orthogonal simulation boxes, the bins are also layers, pencils, or
150
215
boxes aligned with the xyz coordinate axes. For triclinic
204
269
Additional optional keywords also affect the operation of this fix.
206
The {units} keyword determines the meaning of the distance units used
207
for the bin size {delta} and for {origin} if it is a coordinate
208
value. For orthogonal simulation boxes, any of the 3 options may be
209
used. For non-orthogonal (triclinic) simulation boxes, only the
210
{reduced} option may be used.
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A {box} value selects standard distance units as defined by the
213
"units"_units.html command, e.g. Angstroms for units = real or metal.
214
A {lattice} value means the distance units are in lattice spacings.
215
The "lattice"_lattice.html command must have been previously used to
216
define the lattice spacing. A {reduced} value means normalized
217
unitless values between 0 and 1, which represent the lower and upper
218
faces of the simulation box respectively. Thus an {origin} value of
219
0.5 means the center of the box in any dimension. A {delta} value of
220
0.1 means 10 bins span the box in that dimension.
222
Consider a non-orthogonal box, with bins that are 1d layers or slabs
223
in the x dimension. No matter how the box is tilted, an {origin} of
224
0.0 means start layers at the lower "b" cross "c" plane of the
225
simulation box and an {origin} of 1.0 means to start layers at the
226
upper "b" cross "c" face of the box. A {delta} value of 0.1 means
227
there will be 10 layers from 0.0 to 1.0, regardless of the current
228
size or shape of the simulation box.
270
The {region}, {bound}, and {discard} keywords were discussed above.
230
272
The {norm} keyword affects how averaging is done for the output
231
273
produced every {Nfreq} timesteps. For an {all} setting, a bin
270
308
values on steps 8000,9000,10000. Outputs on early steps will average
271
309
over less than M values if they are not available.
311
The {units} keyword determines the meaning of the distance units used
312
for the bin size {delta} and for {origin} and {bounds} values if they
313
are coordinate value. For orthogonal simulation boxes, any of the 3
314
options may be used. For non-orthogonal (triclinic) simulation boxes,
315
only the {reduced} option may be used.
317
A {box} value selects standard distance units as defined by the
318
"units"_units.html command, e.g. Angstroms for units = real or metal.
319
A {lattice} value means the distance units are in lattice spacings.
320
The "lattice"_lattice.html command must have been previously used to
321
define the lattice spacing. A {reduced} value means normalized
322
unitless values between 0 and 1, which represent the lower and upper
323
faces of the simulation box respectively. Thus an {origin} value of
324
0.5 means the center of the box in any dimension. A {delta} value of
325
0.1 means 10 bins span the box in that dimension.
327
Consider a non-orthogonal box, with bins that are 1d layers or slabs
328
in the x dimension. No matter how the box is tilted, an {origin} of
329
0.0 means start layers at the lower "b" cross "c" plane of the
330
simulation box and an {origin} of 1.0 means to start layers at the
331
upper "b" cross "c" face of the box. A {delta} value of 0.1 means
332
there will be 10 layers from 0.0 to 1.0, regardless of the current
333
size or shape of the simulation box.
273
335
The {file} keyword allows a filename to be specified. Every {Nfreq}
274
336
timesteps, a section of bin info will be written to a text file in the
275
337
following format. A line with the timestep and number of bin is
347
409
"compute"_compute.html, "fix ave/atom"_fix_ave_atom.html, "fix
348
410
ave/histo"_fix_ave_histo.html, "fix ave/time"_fix_ave_time.html,
349
411
"variable"_variable.html, "fix ave/correlate"_fix_ave_correlate.html,
412
"fix ave/spatial/sphere"_fix_ave_spatial_sphere.html
353
The option defaults are units = lattice, norm = all, no file output,
354
and ave = one, title 1,2,3 = strings as described above.
416
The option defaults are bound = lower and upper in all dimensions,
417
discard = mixed, norm = all, ave = one, units = lattice, no file
418
output, and title 1,2,3 = strings as described above.