fermi/README.md

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# A minimalist calculator for fermi estimation
This project is a minimalist, stack-based DSL for Fermi estimation. It can multiply and divide scalars, lognormals and beta distributions.
## Motivation
Sometimes, [Squiggle](https://github.com/quantified-uncertainty/squiggle), [simple squiggle](https://git.nunosempere.com/quantified.uncertainty/simple-squiggle) or [squiggle.c](https://git.nunosempere.com/personal/squiggle.c) are still too complicated and un-unix-like.
## Usage
Here is an example
```
$ go run fermi.go
5000000 12000000
=> 5.0M 12.0M
* beta 1 200
1.9K 123.1K
* 30 180
122.9K 11.7M
/ 48 52
2.5K 234.6K
/ 5 6
448.8 43.0K
/ 6 8
64.5 6.2K
/ 60
1.1 103.7
```
Perhaps this example is more understandable with comments and better units:
```
$ sed -u "s|#.*||" | sed -u 's|M|000000|g' | go run fermi.go
5M 12M # number of people living in Chicago
=> 5.0M 12.0M
* beta 1 200 # fraction of people that have a piano
1.9K 123.1K
30 180 # minutes it takes to tune a piano, including travel time
122.9K 11.7M
/ 48 52 # weeks a year pianotuners work for
2.5K 234.6K
/ 6 8 # hours a day
353.9 34.1K
/ 60 # minutes to an hour
5.9 568.3
=: piano_tuners_in_Chicago
piano_tuners_in_Chicago => 5.9 568.3
```
Here is instead an example using beta distributions and variables:
```
1 2
=> 1.0 2.0
* 1_000_000_000
=> 1000.0M 2.0B
=: x # assign to variable
x => 1000.0M 2.0B
. # clear the stack, i.e., make it be 1
beta 1 2
=> beta 1.0 2.0
beta 12 300
=> beta 13.0 302.0
=. y # assign to variable and clear the stack (return it to 1)
y => beta 13.0 302.0
x
=> 1000.0M 2.0B
* y
=> samples 31.3M 98.2M
```
The difference between `=: x` and `=. y` is that `=.` clears the stack after the assignment.
## Installation
```
make build
sudo make install
f # rather than the previous go run fermi.go
```
Why use make instead of the built-in go commands? Because the point of make is to be able to share command-line recipes.
## Usage together with standard Linux utilities
```bash
f
sed -u "s|#.*||" | sed -u 's|M|000000|g' | f
cat more/piano-tuners.f | f
cat more/piano-tuners-commented.f | sed -u "s|#.*||" | sed -u 's|M|000000|g' | f
tee -a input.log | go run fermi.go | tee -a output.log
tee -a io.log | go run fermi.go | tee -a io.log
function f(){
sed -u "s|#.*||" |
sed -u "s|//.*||" |
sed -u 's|K|000|g' |
sed -u 's|M|000000|g' |
sed -u 's|B|000000000|g' |
/usr/bin/f
}
```
Note that these sed commands are just hacks, and won't parse e.g., `3.5K` correctly—it will just substitute for 3.5000
## Tips & tricks
- It's conceptually clearer to have all the multiplications first and then all the divisions
- Sums and divisions now also supported
- For things between 0 and 1, consider using a beta distribution
## Roadmap
- [x] Write README
- [x] Add division?
- [x] Read from file?
- [x] Save to file?
- [x] Allow comments?
- [x] Use a sed filter?
- [x] Add show more info version
- [x] Scalar multiplication and division
- [ ] Program into a small device, like a calculator?
- [-] Think of some way of calling bc
- [x] Think how to integrate with squiggle.c to draw samples
- [x] Copy the time to botec go code
- [x] Define samplers
- [x] Call those samplers when operating on distributions that can't be operted on algebraically
- [ ] Think about how to draw a histogram from samples
- [x] Display output more nicely, with K/M/B/T
- [x] Consider the following: make this into a stack-based DSL, with:
- [x] Variables that can be saved to and then displayed
- [x] Other types of distributions, particularly beta distributions? => But then this requires moving to bags of samples. It could still be ~instantaneous though.
- [x] Figure out go syntax for
- Maps
- Joint types
- Enums
- [x] Fix correlation problem, by spinning up a new randomness thing every time some serial computation is done.
- [ ] Dump samples to file
- [ ] Represent samples/statistics in some other way
- [ ] Perhaps use qsort rather than full sorting
Some possible syntax for a more expressive stack-based DSL (now implemented)