xCoba: General component tensor computer algebra

Authors: David Yllanes and José M. Martín-García, © 2005-2020 under GPL.

Introduction

xCoba, a companion package to xTensor, provides several tools for working with bases and components. It allows the user to define bases on one or more manifolds and to handle basis vectors, using basis indices notation. It performs component calculations such as expanding a tensor in a specified basis, changing the basis of an expression or tracing the contraction of basis dummies. The package knows how to express derivatives and brackets of basis vectors in terms of Christoffel and torsion tensors and how to assign values to the components of a tensor. Support for charts (coordinate fields, restriction of a field to a point, etc.) is still limited.

See xCoba.History.

Download and installation

Current version: 0.8.5 (as of 16 February 2020). It is recommended to download the main xAct bundle, but you can also download the different files separately:

• xCoba.nb: source file with all definitions and comments. Many examples. You need this file if you want to understand and/or modify the internals of the package. This is almost a Reference file.
• xCoba.m: package file. This file is automatically generated by Mathematica when xCoba.nb is saved. This is the only essential file.
• xCobaDoc.nb: main documentation file.
• General Public License

See the Installation notes.