General reference for scuff-em command-line applications

This page collects some general information that applies to many or all of the standalone command-line applications in the scuff-em suite.

1. Common command-line arguments

The various standalone applications in the scuff-em suite share a number of command-line arguments in common, as described below. Not all codes accept all arguments (for example, scuff-transmission does not accept --TransFile), but the format of each arguments is standardized among all codes that do accept that argument.

Options specifying geometry inputs

--geometry MyGeometry.scuffgeo

Specifies the scuff-em geometry file describing your geometry. This option is always mandatory.

--TransFile MyTransformations.trans

Specifies an optional file describing one or more geometrical transformations to be applied to your geometry. Omitting the --TransFile option (when running a code that accepts it) is equivalent to specifying an empty transformation named DEFAULT that leaves the geometry unchanged from the configuration described by the .scuffgeo file.

Options specifying individual frequencies and Bloch vectors at which to calculate

--Omega 3.34 --Omega 4.25+0.9i --Lambda 2.3 --OmegaFile MyOmegaFile --LambdaFile MyLambdaFile

Specifies one or more frequencies at which to perform calculations.

--Omega specifies the angular frequency in units of rad/sec. The argument of --Omega may be a complex number.

The alternative option --Lambda instead specifies the frequency in terms of the corresponding free-space wavelength (where is the vacuum speed of light, irrespective of the material properties of your geometry.) --Lambda values are interpreted in units of microns (m).

The options --OmegaFile or --LambdaFile may be used to specify a file containing one or more --Omega or --Lambda values, one per line (blank lines and comments are ignored.)

--OmegakBlochFile MyOkBFile

Similar to --OmegaFile, but specifies a list of (frequency, Bloch vector) points at which to perform calculations. This option only makes sense when used with extended geometries

The argument specified for --OmegakBlochFile should be a file containing two numbers on each line (for 1D extended geometries) or three numbers on each line (for 2D extended geometries). (Blank lines and comment lines beginning with # are ignored.) The first number on each line is the --Omega value; the next one or two numbers are the components of the 1D or 2D Bloch wavevector, measured in units of (m).

--Xi 0.39 --XiFile MyXiFile --XikBlochFile MyXkBFile

Similar to --Omega, --OmegaFile, and --OmegakBlochFile, but used for codes (scuff-cas3d and scuff-caspol) that perform calculations at pure imaginary frequencies, . Values specified for --Xi should be positive real numbers.

Options specifying evaluation points

--EPFile MyEPFile

For codes that compute spatially-resolved output quantities, this option specifies a file describing a list of spatial evaluation points. (Which output quantity depends on the code you are running; for example, scuff-scatter will report components of the scattered and total fields at the evaluation points, while scuff-neq will report values of the thermally-averaged fluxes of energy and momentum at the evaluation points.)

The argument to --EPFile should be a file containing one or more lines, each of which contains three space-separated numbers (the Cartesian coordinates of the evaluation point). Blank lines and comments (lines beginning with #) are ignored. For example, to ask scuff-scatter for the scattered field components at points on the z axis, the file might look like this:

# evaluation points 0.0 0.0 -2.0 0.0 0.0 -1.9 ... 0.0 0.0 1.9 0.0 0.0 2.0

Options controlling frequency integrations

--OmegaQuadrature [adaptive | cliff] --OmegaMin 0.01 --XiQuadrature [adaptive | cliff] --XiMin 0.01 --AbsTol --RelTol

These arguments affect the behavior of application codes that compute output quantities by performing numerical integrations over angular frequencies---either real angular frequencies or imaginary angular frequencies . (More specifically, scuff-neq performs integrations, while scuff-cas3d and scuff-caspol perform integrations.)

--OmegaQuadrature or --XiQuadrature specify the numerical quadrature algorithm. If these options are left unspecified, an appropriate algorithm is chosen automatically.

--OmegaMin or --XiMin specify the minimum angular frequency at which numerical scuff-em calculations are performed. For cases in which the lower limit of the or integration is 0, the integrand is assumed to be constant between 0 and the value specified here. These options are interpreted in the usual scuff-em frequency units of rad/sec, so typical values will be something like 0.001.

--AbsTol and --RelTol may be used to specify absolute and relative error tolerances for adaptive quadrature algorithms. If an adaptive cubature method seems be spending too much time attempting to achieve high accuracy in a frequency quadrature, try increasing --RelTol to something like 0.1 or even 0.5.

Options controlling Brillouin-zone integrations

--BZQuadrature [adaptive | cliff] --BZSymmetry [adaptive | cliff] --MaxBZSamples 1000;

These arguments affect the behavior of application codes that compute output quantities for periodic geometries by performing numerical integrations over the Brillouin zone. Such codes include scuff-ldos, scuff-neq, scuff-cas3d, and scuff-caspol.

--BZSymmetry may be used for 2D periodic geometries to declare that the Brillouin-zone integrand is symmetric under the interchange .

--MaxBZSamples 1000 may be used to restrict adaptive integration algorithms to a maximum of 1,000 evaluations of the Brillouin-zone integrand.

Miscellaneous options

--FileBase MyFileBase

Specifies the base file name for output files (so that, for example, the frequency-resolved output file written by scuff-cas3d will be MyFileBase.byXi, while the frequency-integrated output file will be MyFileBase.out). If this option is not specified, the file base is taken to be the base filename of the .scuffgeo file.

2. Passing command-line options via text file

All of the standalone applications in the scuff-em suite allow their command-line options to be passed via a text file fed into standard input.

Each line of this text file should consist of a single command-line option (minus the -- at the beginning) followed by any arguments the option might take.

For example, running scuff-scatter with the command-line options

% scuff-scatter --geometry Spheres.scuffgeo --omega 1.0 --pwPolarization 1 0 0 --pwDirection 0 0 1 --EPFile MyEPFile 

is equivalent to running

% scuff-scatter < MyOptionsFile

where the file MyOptionsFile looks like this:

# options for scuff-scatter 
geometry Spheres.scuffgeo
omega 1.0

pwPolarization 1 0 0 
pwDirection 0 0 1

EPFile MyEPFile

Note that blank lines and comments (lines starting with #) are ignored.

You may also combine the two methods of specifying options by passing some options via text file and others on the command line. If there are any conflicts, the values specified on the command line take precedence. For instance, to re-run the example above at a new frequency with everything else unchanged, you could say

 % scuff-scatter --Omega 2.0 < MyOptionsFile

3. Complex numbers

Many of the standalone programs in the scuff-em suite have options for which you may specify complex numbers. (An example is the --omega option accepted by scuff-scatter and other codes, for which you may specify complex or even pure imaginary numbers to do calculations at complex frequencies.)

To specify a complex number as a parameter value, write both the real and imaginary parts together as a single string (no spaces), separated by + or -, with the imaginary part terminated by i or I (you may also use j or J). For example, all of the following are valid frequency specifications:

 --omega 2.3+4.5i
 --omega 2.3
 --omega 4.5j
 --omega 12.3e2+45.4e2I

4. Log files

All command-line codes in the scuff-em suite write logging information to text-based logfiles with extension .log. You can monitor these files to follow the progress of your calculations.

For example, after launching this sample scuff-cas3d run, type the following at a terminal window:

% tail -f SiliconSlabs_L2_40.log

This produces a running list of log messages, something like this:

06/15/15::10:13:40: scuff-cas3D running on superhr1
06/15/15::10:13:40: Added /home/homer/work/scuff-em-sandbox/mshFiles to mesh search path.
06/15/15::10:13:40: Adding lattice basis vector (2,0).
06/15/15::10:13:40: Adding lattice basis vector (0,2).
06/15/15::10:13:40: Computing Casimir integrand at (Xi,kx,ky)=(0.5,0.19635,0.19635)
06/15/15::10:13:49: Computing Casimir integrand at (Xi,kx,ky)=(0.5,0.217586,0.172518)
06/15/15::10:13:51: Computing Casimir integrand at (Xi,kx,ky)=(0.5,0.256543,0.106264)
06/15/15::10:13:52: Computing Casimir integrand at (Xi,kx,ky)=(0.5,0.275845,0.0318681) 

5. Output Files

The scuff-em application codes generally produce output in the form of human-readable text-based data files. The typical naming convention for these files is Geometry.Extension, where Geometry.scuffgeo is the name of the scuff-em geometry file on which the calculation was run, and where Extension is an application-specific file extension that attempts to describe the content of the file; for example, scuff-scatter produces files named Geometry.PFT to report the power, force, and torque on bodies irradiated by external fields. You can use the --filebase command-line option to scuff-em codes to select a base filename other than Geometry.

All text-based data files produced by scuff-em codes should contain a human-readable header at the top of the file explaining how to interpret its content. For example, the first few lines of the .PFT output file produced by scuff-scatter look like this:

# scuff-scatter running on hikari 08/03/15::23:15:45
# data file columns: 
# 1 omega 
# 2 surface label 
# 3 absorbed power (watts)
# 4 scattered power (watts)
# 5 x-force (nanoNewtons)
# 6 y-force (nanoNewtons)
# 7 z-force (nanoNewtons)
# 8 x-torque (nanoNewtons*microns)
# 9 y-torque (nanoNewtons*microns)
# 10 z-torque (nanoNewtons*microns)
0.05 Particle 6.994160e-04 1.562608e-03 -1.120907e-04 7.169210e-03 7.128598e-03 -3.622586e-03 1.005173e-03 9.428114e-02 

If you encounter a situation in which a scuff-em application code fails to write an appropriate file header to an output file, please file an issue on the scuff-em GitHub page.

Other types of output files produced by scuff-em application codes include .hdf5 binary data files and .pp files containing visualization data that may be viewed in gmsh.

6. Environment variables

Here are some environment-variable settings that affect the behavior of scuff-em.

% export SCUFF_GEO_PATH=/path/to/scuffgeo/files
% export SCUFF_MESH_PATH=/path/to/msh/files
% export SCUFF_MATPROP_PATH=/path/to/matprop/files

These environment variables may be used to specify colon-separated lists of directories in which scuff-em will look for various types of input files: [.scuffgeo geometry files][Geometries] (SCUFF_GEO_PATH), .msh surface-mesh files (SCUFF_MESH_PATH), and [material-property files]Materials.

% export SCUFF_LOGLEVEL="NONE"
% export SCUFF_LOGLEVEL="TERSE"
% export SCUFF_LOGLEVEL="VERBOSE"
% export SCUFF_LOGLEVEL="VERBOSE2"

Sets the verbosity of messages written to the .log file.

% export SCUFF_INTERPOLATION_TOLERANCE=1.0e-3

This option, which is only relevant for extended geometries, set an internal tolerance parameter that controls the accuracy with which BEM matrix elements and scattered fields are computed. Its default value is 1.0e-6, but this is probably overly stringent, and may generally be relaxed to 1e-3 or so to reduce memory usage and CPU time without significant accuracy penalties. If your calculation is running out of memory or taking too long to run, try setting it to 1.0e-4 or 1.0e-3. Please tell us about your experiences with this parameter!

(More specifically: scuff-em uses Ewald summation to accelerate the calculation of the periodic Green's function, but even this accelerated calculation is not fast enough to handle the many millions of evaluations needed to assemble the full BEM matrix. For this reason, when assembling the BEM matrix at a given frequency and Bloch vector, scuff-em first precomputes Ewald-summed values of the periodic DGF at grid points of an interpolation grid, after which values are obtained by interpolation (bypassing Ewald summation). The spacing of the grid points is chosen automatically to ensure that the maximum relative error between the interpolated and exact values at any point within the grid boundaries is less than SCUFF_INTERPOLATION_TOLERANCE.

% export OMP_NUM_THREADS="8"
% export GOMP_CPU_AFFINITY="0-7"

These options should not be necessary, but may be needed to ensure that scuff-em takes advantage of all available CPU cores on your system. The former option says that you want to use 8 cores, and the latter option says that you want these 8 cores to be the first 8 available (as opposed to, say, the second set of 8 available cores on a 16-core machine).