Simulation

class emg3d.simulations.Simulation(survey, model, max_workers=4, gridding='single', **kwargs)

Bases: object

Create a simulation for a given survey on a given model.

A simulation can be used to compute responses for an entire survey, hence for an arbitrary amount of sources, receivers, and frequencies. The responses are computed in parallel over sources and frequencies. It can also be used to compute the misfit with the data and to compute the gradient of the misfit function.

The computational grid(s) can either be provided, or automatic gridding can be used; see the description of the parameters gridding and gridding_opts for more details.

Note

The automatic gridding does its best to generate meshes that are suitable for the provided model and survey. However, CSEM spans a wide range of acquisition layouts, and both frequencies and conductivities or resistivities span many orders of magnitude. This makes it hard to have a function that fits all purposes. Check the meshes with your expert knowledge. Also, the automatic gridding is conservative in its estimate, trying to be on the save side (correct results over speed). This means, however, that often smaller grids could be used by providing the appropriate options in gridding_opts or directly providing your own computational grids.

Note

The package xarray has to be installed in order to use Simulation: pip install xarray or conda install -c conda-forge xarray.

Parameters

surveySurvey

The survey; a emg3d.surveys.Survey instance. The survey contains sources, receivers, frequencies, and optionally data.

The survey-data will be modified in place. Provide survey.copy() if you want to avoid this.

modelModel

The model; a emg3d.models.Model instance.

max_workersint, default: 4

The maximum number of processes that can be used to execute the given calls.

griddingstr, default: ‘single’

Method to create the computational grids.

The different methods are:

• 'same': Same grid as for the input model.

• 'single': A single grid for all sources and frequencies.

• 'frequency': Frequency-dependent grids.

• 'source': Source-dependent grids.

• 'both': Frequency- and source-dependent grids.

• 'input': Same as 'single', but the grid has to be provided in gridding_opts instead of being automatically created.

• 'dict': Same as 'both', but the grids have to be provided in gridding_opts in the form of dict[source][frequency] instead of being automatically created.

See the parameter gridding_opts for more details.

gridding_opts{dict, TensorMesh}, default: {}

Input format depends on gridding:

• 'same': Nothing, gridding_opts is not permitted.

• 'single', 'frequency', 'source', 'both': Described below.

• 'input': A emg3d.meshes.TensorMesh.

• 'dict': Dictionary of the format dict[source][frequency] containing a emg3d.meshes.TensorMesh for each source-frequency pair.

The dict in the case of 'single', 'frequency', 'source', 'both’ is passed to emg3d.meshes.construct_mesh; consult the corresponding documentation for more information. Parameters that are not provided are estimated from the provided model, grid, and survey using emg3d.simulations.estimate_gridding_opts, which documentation contains more information too.

There are two notably differences to the parameters described in emg3d.meshes.construct_mesh:

• vector: besides the normal possibility it can also be a string containing one or several of 'x', 'y', and 'z'. In these cases the corresponding dimension of the input mesh is provided as vector. See emg3d.simulations.estimate_gridding_opts.

• expand: in the format of [property_sea, property_air]; if provided, the input model is expanded up to the seasurface with sea water, and an air layer is added. The actual height of the seasurface can be defined with the key seasurface. See emg3d.simulations.expand_grid_model.

solver_optsdict, default: {‘verb’: 2’}

Passed through to emg3d.solver.solve. The dict can contain any parameter that is accepted by the emg3d.solver.solve except for model, sfield, efield, return_info, and log. Default verbosity is verb=2.

verbint, default: 0

Level of verbosity. Possible options:

• -1: Errors.

• 0: Warnings.

• 1: Info.

namestr, default: None

Name of the simulation.

infostr, default: None

Simulation info or any other info (e.g., what was the purpose of this simulation).

Attributes Summary

data	Shortcut to survey.data.
gradient	Return the gradient of the misfit function.
misfit	Return the misfit function.

Methods Summary

clean([what])	Clean part of the data base.
compute([observed])	Compute efields asynchronously for all sources and frequencies.
copy([what])	Return a copy of the Simulation.
from_dict(inp)	Convert dict into emg3d.simulations.Simulation instance.
from_file(fname[, name])	Load Simulation from a file.
get_efield(source, frequency, **kwargs)	Return electric field for given source and frequency.
get_efield_info(source, frequency)	Return the solver information of the corresponding computation.
get_grid(source, frequency)	Return computational grid of the given source and frequency.
get_hfield(source, frequency, **kwargs)	Return magnetic field for given source and frequency.
get_model(source, frequency)	Return model on the grid of the given source and frequency.
print_grid_info([verb, return_info])	Print info for all generated grids.
print_solver_info([field, verb, return_info])	Print solver info.
to_dict([what, copy])	Store the necessary information of the Simulation in a dict.
to_file(fname[, what, name])	Store Simulation to a file.

Attributes Documentation

data

Shortcut to survey.data.

gradient

Return the gradient of the misfit function.

See emg3d.optimize.gradient.

misfit

Return the misfit function.

See emg3d.optimize.misfit.

Methods Documentation

clean(what='computed')

Clean part of the data base.

Parameters

whatstr, default: ‘computed’

What to clean. Possibilities:

• 'computed': Removes all computed properties: electric and magnetic fields and responses at receiver locations.

• 'keepresults': Removes everything except for the responses at receiver locations.

• 'all': Removes everything (leaves it plain as initiated).

compute(observed=False, **kwargs)

Compute efields asynchronously for all sources and frequencies.

Parameters

observedbool, default: False

If True, it stores the current result also as observed model. This is usually done for pure forward modelling (not inversion). It will as such be stored within the survey. If the survey has either relative_error or noise_floor, random Gaussian noise of standard deviation will be added to the data.observed (not to data.synthetic). Also, data below the noise floor will be set to NaN.

min_offsetfloat, default: 0.0

Data points in data.observed where the offset < min_offset are set to NaN.

copy(what='computed')

Return a copy of the Simulation.

See to_file for more information regarding what.

classmethod from_dict(inp)

Convert dict into emg3d.simulations.Simulation instance.

Parameters

inpdict

Dictionary as obtained from emg3d.simulations.Simulation.to_dict.

Returns

simulationSimulation

A emg3d.simulations.Simulation instance.

classmethod from_file(fname, name='simulation', **kwargs)

Load Simulation from a file.

Parameters

fnamestr

Absolute or relative file name including extension.

namestr, default: ‘simulation’

Name under which the simulation is stored within the file.

kwargsKeyword arguments, optional

Passed through to io.load.

Returns

simulationSimulation

A emg3d.simulations.Simulation instance.

infostr, returned if verb<0

Info-string.

get_efield(source, frequency, **kwargs)

Return electric field for given source and frequency.

get_efield_info(source, frequency)

Return the solver information of the corresponding computation.

get_grid(source, frequency)

Return computational grid of the given source and frequency.

get_hfield(source, frequency, **kwargs)

Return magnetic field for given source and frequency.

get_model(source, frequency)

Return model on the grid of the given source and frequency.

print_grid_info(verb=1, return_info=False)

Print info for all generated grids.

print_solver_info(field='efield', verb=1, return_info=False)

Print solver info.

to_dict(what='computed', copy=False)

Store the necessary information of the Simulation in a dict.

See to_file for more information regarding what.

to_file(fname, what='computed', name='simulation', **kwargs)

Store Simulation to a file.

Parameters

fnamestr

Absolute or relative file name including ending, which defines the used data format. See emg3d.io.save for the options.

whatstr, default: ‘computed’

What to store. Possibilities:

• 'computed': Stores all computed properties: electric fields and responses at receiver locations.

• ‘results': Stores only the response at receiver locations.

• 'all': Stores everything.

• 'plain': Only stores the plain Simulation (as initiated).

namestr, default: ‘simulation’

Name with which the simulation is stored in the file.

kwargsKeyword arguments, optional

Passed through to emg3d.io.save.

estimate_gridding_opts Solver