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Wire Cell Interfaces

This package provides a set of abstract base classes aka interface classes. In general, there should be no implementation code in this package although we currently violate that slightly.

Ideally, all implementation classes, besides what is in util/, are based on one or more interface classes in iface/.

Guidelines for adding new interfaces to this subpackage:

  • general in terms of concept (abstract the concept and type)
  • specific in terms of API (fewer methods are better)
  • minimal in terms of dependencies (nothing outside util/ and core dependence)

When adding a new interface which is very specific to an implementation try to remove any special purpose data types. Use Eigen3 arrays instead of libtorch tensors. Use IFrame instead of Eigen3 arrays.

If a new interface must bring in a new dependency then it may be rejected for living in iface/. Developers are free to add interfaces to implementation packages however this will lead to complication in the overall WCT dependency tree. Discussion is warranted in these cases.

See the user manual for more info. https://wirecell.bnl.gov/

Interfaces

IDFT

The IDFT class provides interface to methods to perform discrete Fourier transforms on arrays of complex single precision floating point values.

The interface defines a number of methods which take a general naming convention like:

void <direction><domain>(...);

The “direction” of the transform is one of

fwd
the DFT is from interval to frequency, no normalization.
inv
the DFT is from frequency to interval, 1/n normalization.

The “domain” determines the dimension of array and how it is transformed

1d
a 1D array is transformed
1b
a batch of equal-length 1D arrays are transformed
2d
a 2D array is transformed (along both dimensions)

The shape of 2D arrays (1b or 2d methods) are given in terms of two numbers: stride and nstrides. The number stride counts the number of contiguous array elements along one dimension and nstrides counts the number non-contiguous elements logically along the opposite dimension. In the case of “row-major” aka “C” memory ordering of 2D arrays, the number stride counts the number of elements in one “row” and nstrides counts the number of rows, aka, the number of elements in one column.

The 1b transforms operate along a contiguous array of length stride. By default, these transforms are implemented in terms of nstrides calls to the 1d DFT interface method. The implementation may override the 1b default methods for example to exploit some kind of “batch optimization”.

Limitations

  • The potential speed up when the input to a forward or output from reverse is real valued is not possible to implement with IDFT. It requires the caller to take particular care in array sizes and would double the number of methods.
  • To satisfy the low-level pointer to memory interface from higher level objects see the Waveform.h and Array.h headers in WireCellUtil. In particular, see functions there to lift real to complex or perform memory transforms.
  • Interface to higher order transforms, such as convolutions, are not provided. See Aux::DFT for implementations in terms of an IDFT.

…

Any interfaces not listed above, please see their header file in inc/WireCellIface/ for more information.