Add unit conversion explanation and script #11

The9Cat · 2026-01-21T21:39:40Z

Includes

a LaTeX write up
PDF of the same
Python script for generating conversions
README.md explaining the contents and examples
Example files

Movitation

The EXP drop in on Jan 21, 2026.

Comments

I did try to check all of this, but there may be mistakes...please help check and fix!!
I'm not sure that this helps clarify or makes the confusion worse. LMK what you think.
I hardwired a Gadget and Bonsai unit example in the script but I don't think I have the same units that Jason actually uses, so that would be nice to fix.
Also, if we decide to keep this PR, it would be easy to put in other premade unit stanzas to cover other options. Are there any other that we should put in?

Copilot

Pull request overview

This pull request adds comprehensive documentation and tooling for unit conversions in systems where the gravitational constant G is set to 1, specifically for the EXP simulation code. The PR includes mathematical derivations, a Python conversion script, example data files, and usage documentation.

Changes:

LaTeX document with mathematical derivations for unit conversion formulas
Python script for computing scale factors and converting particle files
Example Earth-Sun system files demonstrating the conversion process

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
EXP-units/expunits.tex	LaTeX documentation explaining unit conversion mathematics and formulas
EXP-units/expunits.py	Python script implementing scale factor calculations and particle file conversion
EXP-units/earth_sun_scaled.txt	Example output file showing Earth-Sun system in scaled units
EXP-units/earth_sun_cgs.txt	Example input file with Earth-Sun system in CGS units
EXP-units/README_expunits.md	Documentation explaining the contents and providing usage examples

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EXP-units/expunits.py

Copilot · 2026-01-21T21:45:37Z

EXP-units/expunits.py

+        if abs((G_check - G_new) / (abs(G_new) if G_new != 0 else 1.0)) > 1e-9:
+            raise ValueError(f"Inconsistent scales: G_new requested {G_new} but scales give {G_check}.")


The condition "abs((G_check - G_new) / (abs(G_new) if G_new != 0 else 1.0)) > 1e-9" will use the denominator 1.0 when G_new is 0, but G_new=0 is not a physically meaningful value for a gravitational constant. Consider raising a more informative error if G_new is 0 or negative before this check.

@copilot open a new pull request to apply changes based on this feedback

Units/expunits.py

EXP-units/expunits.tex

Units/expunits.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot · 2026-01-21T21:47:38Z

@The9Cat I've opened a new pull request, #12, to work on those changes. Once the pull request is ready, I'll request review from you.

Co-authored-by: The9Cat <25960766+The9Cat@users.noreply.github.com>

Add input validation for gravitational constants in compute_scales

Copilot

Pull request overview

Copilot reviewed 5 out of 7 changed files in this pull request and generated 11 comments.

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EXP-units/expunits.py

EXP-units/README.md

Units/expunits.py

EXP-units/expunits.tex

EXP-units/expunits.py

Units/expunits.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot · 2026-01-21T23:44:13Z

@The9Cat I've opened a new pull request, #13, to work on those changes. Once the pull request is ready, I'll request review from you.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Co-authored-by: The9Cat <25960766+The9Cat@users.noreply.github.com>

Add Motivation section to EXP-units README

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Added details about phase-space conversion and provided a Python script for unit conversion.

Updated README to reflect focus on EXP unit conversion for G=1 and clarified example context.

Updated example commands and explanations in README.md for clarity.

Updated section headers and clarified output descriptions.

Updated example usage and detailed explanation of flags in README.

Add unit conversion explanation and script

6ca6b8d

The9Cat requested a review from Copilot January 21, 2026 21:39

Copilot started reviewing on behalf of The9Cat January 21, 2026 21:40 View session

The9Cat assigned JASHunt and michael-petersen Jan 21, 2026

Rename the README.md so that it's picked up automatically by github

f71b901

Copilot AI reviewed Jan 21, 2026

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The9Cat and others added 2 commits January 21, 2026 16:46

Update EXP-units/expunits.py

af40183

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Initial plan

d53f9d0

Copilot AI mentioned this pull request Jan 21, 2026

Add input validation for gravitational constants in compute_scales #12

Merged

Copilot AI and others added 7 commits January 21, 2026 21:50

Add validation for G_new to check for non-positive values

bca5c80

Co-authored-by: The9Cat <25960766+The9Cat@users.noreply.github.com>

Add __pycache__ to .gitignore and remove cached files

744705a

Co-authored-by: The9Cat <25960766+The9Cat@users.noreply.github.com>

Corrected documentation at top of script

613cea2

Merge branch 'units' of github.com:EXP-code/EXP-examples into units

eefd141

Add validation for G_old to prevent division errors

83cde97

Co-authored-by: The9Cat <25960766+The9Cat@users.noreply.github.com>

Simplify division by G_new since it's guaranteed positive

c28a276

Co-authored-by: The9Cat <25960766+The9Cat@users.noreply.github.com>

Merge pull request #12 from EXP-code/copilot/sub-pr-11

0e536a6

Add input validation for gravitational constants in compute_scales

The9Cat requested a review from Copilot January 21, 2026 21:56

Copilot started reviewing on behalf of The9Cat January 21, 2026 21:57 View session

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The9Cat and others added 4 commits January 21, 2026 18:43

Update EXP-units/expunits.py

b8e50d6

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Update EXP-units/README.md

8522c4f

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Update EXP-units/expunits.tex

43d57e6

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Initial plan

dc75160

Copilot AI mentioned this pull request Jan 21, 2026

Add Motivation section to EXP-units README #13

Merged

The9Cat and others added 3 commits January 21, 2026 18:44

Update EXP-units/expunits.py

362f1df

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Update EXP-units/expunits.tex

f8b82c4

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Update EXP-units/expunits.py

14bba61

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot AI and others added 18 commits January 21, 2026 23:47

Add Motivation section to EXP-units README

7533344

Co-authored-by: The9Cat <25960766+The9Cat@users.noreply.github.com>

Comment the header on the refereence example

9ebe729

Merge pull request #13 from EXP-code/copilot/sub-pr-11

a52ccb8

Add Motivation section to EXP-units README

Merge branch 'units' of github.com:EXP-code/EXP-examples into units

3c3fbe5

Updated some wording

e451d30

Update EXP-units/expunits.py

ca21fb2

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Update EXP-units/expunits.py

c82ec51

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Rename directory

e904476

Update README with additional files and examples

af311ef

Update README with phase-space conversion details

2cc793a

Added details about phase-space conversion and provided a Python script for unit conversion.

Revise README for EXP unit conversion details

ed125fb

Updated README to reflect focus on EXP unit conversion for G=1 and clarified example context.

Revise example commands and explanations in README

6aaf326

Updated example commands and explanations in README.md for clarity.

Update README for example usage section

844c36e

Revise README for clarity on checks and outputs

b484a7c

Updated section headers and clarified output descriptions.

A few minor changes to comments after a read through

18d31b1

Merge branch 'units' of github.com:EXP-code/EXP-examples into units

da2e28e

Enhance README with detailed examples and flags

442eff2

Updated example usage and detailed explanation of flags in README.

Add Units utility description to README

0a6d78d

		if abs((G_check - G_new) / (abs(G_new) if G_new != 0 else 1.0)) > 1e-9:
		raise ValueError(f"Inconsistent scales: G_new requested {G_new} but scales give {G_check}.")

Add unit conversion explanation and script #11

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The9Cat commented Jan 21, 2026 •

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