Physics Computing

Python Common Entities for Science (PyCES)

PyCES is a project to develop a standard set of objects and classes for scientific computing using the Python object-oriented scripting language. Initially, PyCES is concentrating on basic physical entities and properties (such as abstract particles, quantities, and vectors). It will expand to deal with more complex entities, such as macroscopic bodies, fluids, molecules, atoms, and nuclei in the future. The eventual goal is to have a set of useful foundation classes describing all entities encountered in scientific computing.

Python, rather than a system programming language like C++ or Java, is used for several reasons:

Objects are cleanly distinguished from functional implementation. Classes and objects belong to the scripting layer, while computer-intensive "number crunching" is performed by efficient C functions.
Python is platform independent (like Java), but is also open source and freely available.
Existing C and C++ functions can be embedded in Python scripts
Graphical user interfaces (Python/Tkinter, wxPython) are available

The distinction of the object and functional layers parallels the three-tier architectures used in business applications, where the user interface, object set, and database implementation are kept distinct. The use of an intermediate object layer provides a standard interface to the database, which can be modified without requiring changes in the user interface and vice-versa. In like fashion, PyCES separates the objects which are used to model a physical system from implementation details of functions used to operate on the objects.

PyCES version 0.10 has the following classes and modules available (see the PyCES Programmer's Guide for more details):

particle Particle class: abstract physical particles with mass, position, and velocity

physconst Defines useful physical constants such as the speed of light, Planck's constant,etc., with units

pyces Imports all PyCES modules

pycesutl Utility functions used by other PyCES modules

quantity Quantity class: base class for all quantities -- numerical value + units

scalar Defines specific scalar quantities, such as Time, Mass, Length, Energy, etc.

spstate SpatialState class: encapsulates time, position, and velocity

units Units class: base class for all units of measure

uomutil Unit of measure conversion utilities for output formatting, etc.

vector Defines specific vector quantities, such as Position, Velocity, Momentum, Force, etc.

PyCES version 0.10 uses the Numerical Python package for its vector and matrix operations. You can set PyCES quantity values from NumPy array objects and use the Numerical Python array processing functions on PyCES quantities.

PyCES is an open source project, and thus will have frequent revisions.
You can download the current version of PyCES from the MICPC software download page.

XML in Physics

The eXtensible Markup Language (XML) is quickly emerging as the lingua franca of the Internet and computing. Going beyond HTML to provideways of marking content and meaning, XML is simpler to use than its parent, SGML (Standard General Markup Language). Major efforts are underway, mostly in the electronic commerce and publishing arenas, to develop XML standards capturing both the syntax and semantics of documents and data. The capabilities of XML point to several possible applications for physics:

Standard data formats: define a set of standard XML formats for physics data; also be able to define XML templates for non-XML data.
Document formats: standard formats for publication of physics articles.
Physics semantics: capture the basic concepts used in physics.

The concentration of the MICPC is on this last category. The complete set of XML representations of physics concepts is termed "Physics Markup Language", or PhysicsML. It is an effort that runs closely parallel to that of PyCES (as discussed above). Such "physics metadata" include:

abstract entities: particles, extended bodies, fluids, ...
concrete entities: electrons, protons, cubic lattices, ...
space and time
measurements and units
forces and relations: electromagnetism, momentum, ...

The first version of the PhysicsML Document Type Definition (DTD) will be available in the near future.

Links to related XML sites

MathML (Mathematics Markup Language). PhysicsML will use MathML for all representation of mathematics
AML Astronomy Markup Language: astronomy related information
W3C XML site Central location for on-line XML resources

Few and Many Body Problems

The MICPC has a strong interest in developing a unified framework for the modeling and simulation of the few and many body problem, both classical and quantum. Future extensions to PyCES are intended to provide a modeling framework for such investigations

Physics Computing Links

particle	Particle class: abstract physical particles with mass, position, and velocity
physconst	Defines useful physical constants such as the speed of light, Planck's constant,etc., with units
pyces	Imports all PyCES modules
pycesutl	Utility functions used by other PyCES modules
quantity	Quantity class: base class for all quantities -- numerical value + units
scalar	Defines specific scalar quantities, such as Time, Mass, Length, Energy, etc.
spstate	SpatialState class: encapsulates time, position, and velocity
units	Units class: base class for all units of measure
uomutil	Unit of measure conversion utilities for output formatting, etc.
vector	Defines specific vector quantities, such as Position, Velocity, Momentum, Force, etc.