Units¶

This package provides unit conversion tools

In [1]:

# Useful for debugging
%load_ext autoreload
%autoreload 2

# Useful for debugging %load_ext autoreload %autoreload 2

In [2]:

from pmd_beamphysics import particle_paths
from pmd_beamphysics.units import dimension_name, sqrt_unit, known_unit
from h5py import File

from pmd_beamphysics import particle_paths from pmd_beamphysics.units import dimension_name, sqrt_unit, known_unit from h5py import File

This is the basic class:

In [3]:

?pmd_unit

?pmd_unit

Object `pmd_unit` not found.

Get a known units. These can be multiplied and divided:

In [4]:

u1 = known_unit["J"]
u2 = known_unit["m"]
u1, u2, u1 / u2, u1 * u2

u1 = known_unit["J"] u2 = known_unit["m"] u1, u2, u1 / u2, u1 * u2

Out[4]:

(pmd_unit('J', 1, (2, 1, -2, 0, 0, 0, 0)),
 pmd_unit('m', 1, (1, 0, 0, 0, 0, 0, 0)),
 pmd_unit('J/m', 1.0, (1, 1, -2, 0, 0, 0, 0)),
 pmd_unit('J*m', 1, (3, 1, -2, 0, 0, 0, 0)))

Special function for sqrt:

In [5]:

sqrt_unit(u1)

sqrt_unit(u1)

Out[5]:

pmd_unit('\sqrt{ J }', 1.0, (1.0, 0.5, -1.0, 0.0, 0.0, 0.0, 0.0))

openPMD HDF5 units¶

Open a file, find the particle paths from the root attributes

In [6]:

# Pick one:
# H5FILE = 'data/bmad_particles.h5'
H5FILE = "data/distgen_particles.h5"
# H5FILE = 'data/astra_particles.h5'
h5 = File(H5FILE, "r")

ppaths = particle_paths(h5)
print(ppaths)

# Pick one: # H5FILE = 'data/bmad_particles.h5' H5FILE = "data/distgen_particles.h5" # H5FILE = 'data/astra_particles.h5' h5 = File(H5FILE, "r") ppaths = particle_paths(h5) print(ppaths)

['//']

This points to a single particle group:

In [7]:

ph5 = h5[ppaths[0]]
list(ph5)

ph5 = h5[ppaths[0]] list(ph5)

Out[7]:

['momentum', 'particleStatus', 'position', 'time', 'weight']

Each component should have a dimension and a conversion factor to SI:

In [8]:

d = dict(ph5["momentum/x"].attrs)
d

d = dict(ph5["momentum/x"].attrs) d

Out[8]:

{'unitDimension': array([ 1,  1, -1,  0,  0,  0,  0]),
 'unitSI': np.float64(5.344285992678308e-28),
 'unitSymbol': 'eV/c'}

In [9]:

tuple(d["unitDimension"])

tuple(d["unitDimension"])

Out[9]:

(np.int64(1),
 np.int64(1),
 np.int64(-1),
 np.int64(0),
 np.int64(0),
 np.int64(0),
 np.int64(0))

This will extract the name of this dimension:

In [10]:

dimension_name(d["unitDimension"])

dimension_name(d["unitDimension"])

Out[10]:

'momentum'

Nice arrays¶

In [11]:

from pmd_beamphysics.units import nice_array

from pmd_beamphysics.units import nice_array

This will scale the array, and return the appropriate SI prefix:

In [12]:

x = 1e-4
unit = "m"
nice_array(x)

x = 1e-4 unit = "m" nice_array(x)

Out[12]:

(np.float64(100.00000000000001), np.float64(1e-06), 'µ')

In [13]:

nice_array([-0.01, 0.01])

nice_array([-0.01, 0.01])

Out[13]:

(array([-10.,  10.]), np.float64(0.001), 'm')

In [14]:

from pmd_beamphysics.units import nice_scale_prefix

from pmd_beamphysics.units import nice_scale_prefix

In [15]:

nice_scale_prefix(0.009)

nice_scale_prefix(0.009)

Out[15]:

(np.float64(0.001), 'm')

Limitations¶

This is a simple class for use with this package. So even simple things like the example below will fail.

For more advanced units, use a package like Pint: https://pint.readthedocs.io/

In [16]:

try:
    u1 / 1
except AttributeError:
    print("you cannot do this")

try: u1 / 1 except AttributeError: print("you cannot do this")

you cannot do this