MathParseC-

Another ultrafast repo I'm using to study for math class in a roundabout way (I don't want to study but I want to program and this is math related. Gonna use it to approximate some fourier series)

Purpose

The goal of this repo is to take in string math expressions containing variables and then evaluate them at different points.

Functionality

As of last updating the readme, it supports addition, subtraction, multiplication, division, exponentiation (including sqrts), sine, and cosine. The expression grammar is given in interpreter.h at the top. The great thing about this program is it's super easy to add any new functionality you want by just extending the lexer to parse it and then the interpreter to evaluate it.

Implicit multiplication (e.g. 2sin(3)x) is not supported in the current version (should be 2*sin(3)*x), because I don't really need it. If you want to add it though, just change the grammar and go for it. It works surprisingly well as is and could definitely be useful to someone, so make it yours.

How to use

There's a lexer class that gets fed in a string and then has a get_next_token method that returns tokens from said string, one at a time. There's an interpreter class that takes in that lexer, grabs all its tokens, and then can evaluate the mathematical expression given some input variables stored in an unordered_map. The repo is designed such that you parse the string once with the lexer and then used the parsed data multiple times with the interpreter to speed up execution. Example usage:

//Assign variables
std::unordered_map<std::string, double> vars;
vars["x"] = 5;
vars["pi"] = 3.14159265359;
vars["e"] = 2.71828182846;

//Create lexer and feed it into interpreter
lexer lex("3*sin(pi/2)+e^sin(x)-1/2+5^(1/2)");
interpreter inter;
inter.fetch_tokens(lex);

//Evaluate at multiple values of x
std::cout << inter.interpret(vars) << std::endl; //5.11937
vars["x"] = 2;
std::cout << inter.interpret(vars) << std::endl; //7.21865

Also, make sure to compile with C++11 or higher!

How to install

Clone it, go into the folder, and then

mkdir build
cd build
cmake ..
make
sudo make install

... and make sure to compile future programs with -lcmathparse

Todo

Right now all my expressions are just std::runtime_error because it was easiest. I want to change that and add some comments into the code. After that, I'll add some more functions.

Credit

Credit where credit is due. I learned about lexers and interpreters from this lovely tutorial that teaches you how to build a Pascal interpreter in Python.