# Equation

Solve math expressions or create equations for repeated and complex Math tasks.

To use in browser, download `equation.min.js`

.

*A similar library I wrote in Haskell is also available mathexpr*

Install using npm:

```
npm install equations
```

####Examples:

```
// solve
console.log(Equation.solve('4 * lg(4) ^ 3')); // 32
// equation
let sphereArea = Equation.equation('4 * PI * r^2');
console.log(sphereArea(5)); // 314.1592653589793
let test = Equation.equation('2x + 6y');
console.log(test(4, 3)).to.equal(8 + 18);
```

You can also register your own operators and constants.

```
// these options are explained in [`operators.js`](https://github.com/mdibaiee/Equation/blob/master/lib/operators.js).
Equation.registerOperator('$', {
fn: a => 1/a,
format: '10',
precedence: 2
});
Equation.solve('$2'); // 0.5
Equation.solve('$5'); // 0.2
Equation.registerConstant('N', () => {
return Math.random() * 10 + 10
});
Equation.solve('N'); // a number between 10 and 20
// Complex operators
Equation.solve('sigma(0, 5, 2@ + 5)'); // 60
```

For a list of operators and constants see `operators.js`

and `constants.js`

.

# API

####solve(expression: String) Takes a math expression and evaluates it, returning the result.

####equation(expression: String) Takes a math expression containing variables, returning a function which replaces the variables with given arguments, and solves the expression.

####registerOperator(key: String, options: Object) Registers a new operator.

Options:

#####fn The function which is run on arguments and returns the result #####format The format which specifies how arguments are placed relative to operator, this is a string in which 1 represents the operator and zeroes represent arguments.

For example `+`

has the format `010`

and factorial has `01`

.
#####precedence
Specifies the precedence of operator. The less the value, the higher the precedence, resulting in sooner execution.

####registerConstant(key: String, value: Function/Number) Registers a new constant. value can be a function (takes no arguments), or a constant number.

That's right, we have named these *constants* but they actually can change, that's why we can use functions to define them. An example is the `RAND`

constant which calls `Math.random`

.

# Contributing

The code is commented and I hope you don't have a hard time contributing, anyway, some tips about contributing:

The source code is in `lib`

directory and is then transpiled into `dist`

.

#####Grunt Tasks
######default
Transpiles `lib`

to `dist`

######build
Transpiles, browserifies, uglifies
######eslint
Runs ESLint on `lib`

and `tests`

######test
Runs the tests

Please make sure to run `grunt eslint`

before commiting.

If you're adding something new, please add a test, too.