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, divide, add and substract 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.
## Installation
```
make build
sudo make install
fermi
```
## Usage
```
$ fermi
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:
```
$ fermi
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:
```
$ fermi
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.
If you type "help", you can see a small grammar:
```
$ fermi
help
Operation | Variable assignment | Special
Operation: operator operand
operator: (empty) | * | / | + | -
operand: scalar | lognormal | beta | variable
lognormal: low high
beta: beta alpha beta
Variable assignment: =: variable_name
Variable assignment and clear stack: =. variable_name
Special:
Clear stack: clear | c | .
Print this help message: help | h
Print debug info: debug | d
Exit: exit | e
Comment: # this is a comment
Examples:
+ 2
/ 2.5
* 1 10 (interpreted as lognormal)
+ 1 10
* beta 1 10
1 10 (multiplication taken as default operation)
=: x
.
1 100
+ x
# this is a comment
* 1 12 # this is an operation followed by a comment
exit
```
## Tips & tricks
- It's conceptually clearer to have all the multiplications first and then all the divisions
- For things between 0 and 1, consider using a beta distribution
## Different levels of complexity
The top level f.go file (400 lines) has a bunch of complexity: variables, parenthesis, samples, beta distributions. In the simple/ folder:
- f_simple.go (370 lines) strips variables and parenthesis, but keeps beta distributions, samples, and addition and substraction
- f_minimal.go (140 lines) strips everything that isn't lognormal and scalar multiplication and addition, plus a few debug options.
## Roadmap
Done:
- [x] Write README
- [x] Add division?
- [x] Read from file?
- [x] Save to file?
- [x] Allow comments?
- [x] Use a sed filter?
- [x] Add proper comment processing
- [x] Add show more info version
- [x] Scalar multiplication and division
- [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
- [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] Added bags of samples to support addition and multiplication of betas and lognormals
- [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.
- [x] Clean up error code. Right now only needed for division
- [x] Maintain *both* a more complex thing that's more featureful *and* the more simple multiplication of lognormals thing.
- [x] Allow input with K/M/T
To (possibly) do:
- [ ] Document parenthesis syntax
- [ ] Add functions. Now easier to do with an explicit representation of the stakc
- [ ] Think about how to draw a histogram from samples
- [ ] Dump samples to file
- [ ] Represent samples/statistics in some other way
- [ ] Perhaps use qsort rather than full sorting
- [ ] Program into a small device, like a calculator?
Discarded:
- [ ] ~~Think of some way of calling bc~~