TBD

(Note: "TBD" is the actual name, not a placeholder.)

An equation solver that solves for all the To Be Determined values in a system of equations.

Features

• Employs "direct" solutions where possible.
• All values track units.
• Ability to define new units.
• Graphviz integration for for debugging.
• Find solutions with a minimum number of free variables (coming soon).

Examples

Values can be pinned, with units:

W := 1 [kg];
X := 5 [m];
Y := 7.3 [s];

New units can be defined:

[furlong]   := 660 [ft];
[firkin]    := 90  [lb];
[fortnight] := 336 [hr];

Equations use (more or less) standard C grammar:

V = X / Y;
V / Y = Z;

Exponential use the ^ operator and are required to have constant integral exponents.

E = W * V^2 / 2;

With the exception of unit definitions, the order in which statements are defined is not relevant.

Limitations/Bugs

I'm still working on things so there are some things that are know to not work fully yet:

• Dependent systems of equations: Currently only direct propagation is well supported. A Newton-Raphson solver for systems of equations is implemented, but not well tested.
• Even roots: To avoid dealing with the +/- issue, only odd roots are solved for.

Future work

• Value hints as starting points.
• Rational exponents.
• Macro instantiation.
• Code generator to allow use in other programs.
• Optimization:
  • Merging of equivalent expression sub trees.
  • Conversion between repeated + and * and between repeated * and ^.

Bazel/skylark rules to process .tbd files.

MODULE.bazel

bazel_dep(
    name = "com_github_bcsgh_tbd",
    version = ...,
)

gen_tbd

load("@com_github_bcsgh_tbd//tbd:rule.bzl", "gen_tbd")

gen_tbd(name, srcs, cpp, dot, out, warnings_as_errors)

Process a .tbd file.

PARAMETERS

Name	Description	Default Value
name	The target name.	None
srcs	The input file.	None
cpp	If set, generate a C++ implementation at the give location.	None
dot	If set, generate a graphviz depiction at the give location.	None
out	Output the resolved values at the give location.	None
warnings_as_errors	Fail on warnings.	False

Setup (for development)

To configure the git hooks, run ./.git_hooks/setup.sh