time-to-botec/README.md

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# Time to BOTEC
## About
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This repository contains example of very simple code to manipulate samples in various programming languages. It implements this platonic estimate:
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```
p_a = 0.8
p_b = 0.5
p_c = p_a * p_b
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dists = [0, 1, 1 to 3, 2 to 10]
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weights = [(1 - p_c), p_c/2, p_c/4, p_c/4 ]
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result = mixture(dists, weights) # should be 1M samples
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mean(result)
```
As of now, it may be useful for checking the validity of simple estimations. The title of this repository is a pun on two meanings of "time to": "how much time does it take to do x", and "let's do x".
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## Current languages
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- [x] C
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- [x] Javascript (NodeJS)
- [x] Squiggle
- [x] R
- [x] Python
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- [x] Nim
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## Performance table
With the [time](https://man7.org/linux/man-pages/man1/time.1.html) tool, using 1M samples:
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| Language | Time |
|----------------------|-----------|
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| Nim | 0m0.068s |
| C | 0m0.292s |
| Javascript (NodeJS) | 0m0,732s |
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| Squiggle | 0m1,536s |
| R | 0m7,000s |
| Python (CPython) | 0m16,641s |
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## Notes
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I was really happy trying [Nim](https://nim-lang.org/), and as a result the Nim code is a bit more optimized and engineered:
1. It is using the fastest "danger" compilation mode.
2. It has some optimizations: I don't compute 1M samples for each dist, but instead pass functions around and compute the 1M samples at the end
3. I define the normal function from scratch, using the [BoxMuller transform](https://en.wikipedia.org/wiki/Box%E2%80%93Muller_transform#Basic_form).
4. I also have a version in which I define the logarithm and sine functions themselves in nim to feed into the Box-Muller method. But it is much slower.
Without 1. and 2., the nim code takes 0m0.183s instead. But I don't think that these are unfair advantages: I liked trying out nim and therefore put in more love into the code, and this seems like it could be a recurring factor.
For C, I enabled the `-Ofast` compilation flag. Without it, it instead takes ~0.4 seconds. Initially, before I enabled the `-Ofast` flag, I was surprised that the Node and Squiggle code were comparable to the C code. Using [bun](https://bun.sh/) instead of node is actually a bit slower.
For the Python code, it's possible that the lack of speed is more a function of me not being as familiar with Python. It's also very possible that the code would run faster with [PyPy](https://doc.pypy.org).
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## Languages I may add later
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- [ ] Julia (TuringML)
- [ ] Rust
- [ ] Lisp
- [ ] Stan
- [ ] Go
- [ ] Zig
- [ ] Forth
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- ... and suggestions welcome
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## Roadmap
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The future of this project is uncertain. In most words, I simply forget about this repository.
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To do:
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- [ ] Check whether the Squiggle code is producing 1M samples. Still not too sure.
- Differentiate between initial startup time (e.g., compiling, loading environment) and runtime. This matters because startup time could be ~constant, so for larger projects only the runtime matters.
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## Other similar projects
- Squigglepy: <https://github.com/rethinkpriorities/squigglepy>
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- Simple Squiggle: <https://github.com/quantified-uncertainty/simple-squiggle>