# boldtensors — Modernized Bold Tensor Notation for LaTeX

**Version:** 2.2
**Date:** 2026-05-21
**Authors:** Werner Fink & Jürgen Bachteler
**License:** GNU General Public License, version 2 (GPLv2)

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## Description

The `boldtensors` package provides a highly efficient shorthand for typesetting Latin and Greek characters in bold and blackboard-bold layouts. It is specifically designed for the requirements of Theoretical Physics and General Relativity, where a clear visual distinction between geometric tensor objects and their components or scalars is essential.

The package uses active characters (`~` and `"`) to keep the source code clean and readable:
- `` `$~T$` `` produces a bold tensor $\boldsymbol{T}$.
- `` `$"R$` `` produces a blackboard-bold symbol $\mathbb{R}$.

### Key Features:
- **Engine Independent:** Fully compatible with both classical **pdfLaTeX** (using NFSS) and modern **LuaLaTeX** (using `unicode-math` and OpenType fonts).
- **ISO Compliance:** Includes the `bt-isodiff` sub-package for upright differential operators according to ISO 80000-2.
- **Accurate Metrics:** Correct placement of subscripts, superscripts, and accents (like `\hat{~T}`) by using native math characters instead of boxes.
- **Micro-Typography:** Preserves perfect kerning and font-specific metrics.

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## Files in this Distribution

- `boldtensors.sty`: The main LaTeX package.
- `bt-isodiff.sty`: Independent package for upright ISO differentials (can be used separately).
- `boldtensors.tex`: Documentation source and example file.
- `boldtensors.pdf`: Compiled documentation.
- `README.md`: This file.

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## Installation

1. Copy `boldtensors.sty` and `bt-isodiff.sty` into your local TeX directory (e.g., `~/texmf/tex/latex/boldtensors/`).
2. Update your filename database (e.g., run `texhash` or use your TeX distribution's GUI).
3. In your LaTeX preamble, add:
   ```latex
   \usepackage[nabla,differential]{boldtensors}
## Usage
### Bold Tensors
Use the tilde ~ inside math mode to make the following character bold:

`` `$~A + ~B = ~C$` ``

`` `~\alpha_{\mu\nu}` ``

`` `~\partial_i` `` (Bold partial derivative)

### Blackboard Bold
Use the double quote " for blackboard symbols:

`` `$"R, "C, "N$` ``

### Differential Operators (ISO)
When the differential option is used, the character d is automatically
rendered upright:

`` `$ds^2 = g_{\alpha\beta} dx^{\alpha} dx^{\beta}$` ``

## History
1995: Original version by Werner Fink and Jürgen Bachteler
      at the Institute for Theoretical and Applied Physics,
      University of Stuttgart.

2007: Maintenance update.

2026: Full modernization for LuaLaTeX/OpenType-Math and ISO 80000-2 compliance.
      Rename ``isodiff.sty`` to ``bt-isodiff.sty``

## License
Copyright (C) 1995-2026 Werner Fink.

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your option)
any later version.