meme

A python wrapper for the MEME services at SLAC. The meme wrapper aims to hide away EPICS v4 boilerplate code where possible, and provide a simple API for interacting with the various MEME (MAD EPICS MATLAB Environment) services.

meme is split up into sub-modules, one for each MEME service. So far, the services implemented in python are:

• archive: Use the MEME archive service to get history data for one or more PVs.
• model: Use the MEME model service get machine model data (R-matrices, Twiss parameters, Z-Positions) for beamline elements.
• names: Use the MEME directory service to list PVs, element names, or device names.

Archive

Getting history data via MEME is very straightforward. There is only one method:

>>> import meme.archive
>>> meme.archive.get(["MC00:ASTS:OUTSIDET", "PWR:MCC0:1:SITE"], from_time="1 day ago", to_time="now")
<Results snipped>

You can supply a list of PVs, or just a single PV. The from_time and to_time parameters can take strings of the form "1 day ago", python datetime objects, or a mix:

>>> from datetime import datetime
>>> import meme.archive
>>> downtime_2016 = datetime(2016, 12, 20)
>>> meme.archive.get("GDET:FEE1:241:ENRC", from_time="1 year ago", to_time=downtime_2016)
<Results snipped>

Model

Interacting with the model takes an object oriented approach. To get model data, first make an instance of the Model class, then call its methods to get the data you are interested in. Model must be given a path.The path can be "CU_HXR", "CU_SXR","CU_SPEC", "SC_DIAG0", "SC_BSYD", "SC_HXR", "SC_SXR", or "FACET2E". It can also be givena model_source (for FACET this must be LUCRETIA. The default is BMAD).

>>> from meme.model import Model
>>> m = Model('CU_HXR','BMAD')
>>> m.get_rmat('BPMS:LI24:801')
<6x6 np.ndarray>

The model module works this way to keep things fast: usually, its faster to get the full machine model once, then refer to it repeatedly, than it is to repeatedly ask the model service for small bits of information. Whenever you make a new instance of Model, you'll get the latest data from the service. If you'd like to refresh the data for an existing instance, you can do that by calling Model.refresh_all():

>>> from meme.model import Model
>>> m = Model('CU_HXR')
>>> twiss = m.get_twiss('QUAD:LTU1:440')
>>> m.refresh_all() #The beam energy has changed and you want a new model.
>>> new_twiss = m.get_twiss('QUAD:LTU1:440')

The various get methods in the Model class are pretty flexible. You can input a list of names, a single name, etc. See the documentation for all the details.

Names

Getting lists of PV names is easy. If you know how to use aidalist, you know how to use meme.names.list_pvs():

>>> import meme.names
>>> all_bpm_tmit_pvs = meme.names.list_pvs("BPMS:%:%:TMIT")
<list of BPM TMIT PVs>

The directory service is very powerful, and lets you do fancy queries with sorting and filtering. You can specify a tag to search for, like an LCLS region:

>>> import meme.names
>>> L2_xcor_bacts = meme.names.list_pvs("XCOR:%:BACT", tag="L2", sort_by="z")
<list of XCOR BACT values for L2>

You can also get device names, or element names (aka MAD names), using the list_devices() and list_elements() functions. They take the same arguments as list_pvs(). To get a list of all BPM devices in the 'BSYLTU' line:

>>> import meme.names
>>> bsy_ltu_bpms = meme.names.list_devices("BPMS:%", tag="BSYLTU", sort_by="z")
['BPMS:BSYH:445', 'BPMS:BSYH:465', ...]