# math-problems

Solve math problems easily with this utility library. Includes temperature conversions, geometric area calculations, number utilities, and population statistics.

## Installation

```bash
npm install math-problems
```

## Usage

```javascript
import {
  area,
  toCelsius,
  isEven,
  populationDensity,
  population,
} from 'math-problems';

// Calculate the area of a circle with radius 5
console.log(area.circle(5)); // 78

// Convert 73°F to Celsius
console.log(toCelsius(73)); // 22.777... (repeating decimal)

// Check if a number is even
console.log(isEven(4)); // true

// Calculate population density
console.log(populationDensity(11452000, 1483)); // 7724

// Access population data
console.log(population.br.sp); // 11452000
```

## API Documentation

### 📐 Area Calculations

All area functions return an object with a floored `area` value.

- **Rectangle**  
  `rect(base: number, height: number)`  
  `area.rect(4, 5) ➔ 20`

- **Triangle**  
  `triangle(base: number, height: number)`  
  `area.triangle(4, 5) ➔ 10`

- **Rhombus**  
  `rhombus(D: number, d: number)`  
  `area.rhombus(8, 6) ➔ 24`

- **Trapezoid**  
  `trapezoid(B: number, b: number, height: number)`  
  `area.trapezoid(10, 6, 5) ➔ 40`

- **Circle**  
  `circle(radius: number)`  
  `area.circle(3) ➔ 28`

### 🌡️ Temperature Conversions

Convert between Celsius (°C), Fahrenheit (°F), and Kelvin (K).

- **toCelsius**  
  `toCelsius(temperature: number, unit?: 'F' | 'K')`  
  Default unit: Fahrenheit  
  `toCelsius(32) ➔ 0`  
  `toCelsius(273.15, 'K') ➔ 0`

- **toFahrenheit**  
  `toFahrenheit(temperature: number, unit?: 'C' | 'K')`  
  Default unit: Celsius  
  `toFahrenheit(0) ➔ 32`  
  `toFahrenheit(273.15, 'K') ➔ 32`

- **toKelvin**  
  `toKelvin(temperature: number, unit?: 'C' | 'F')`  
  Default unit: Celsius  
  `toKelvin(0) ➔ 273`  
  `toKelvin(32, 'F') ➔ 273`

### 🔢 Number Utilities

- **isEven(number)**  
  Returns `true` if the number is even.

- **isOdd(number)**  
  Returns `true` if the number is odd.

- **difference(x, y)**  
  Returns the floored difference between two numbers.  
  `difference(10, 3.8) ➔ 6`

- **PI**  
  Math.PI constant (≈3.14159).

### 📊 Interpoolation and regression

- **interpolation(input: { function: (number) => number, value: number, points: number[] })**  
  Interpolates a set of data points from a function and value through Newton Interpolation.

```js
interpolation({
  function: Math.log,
  value: 2,
  points: [1, 4, 6]
})

➔ 0.5658443469009827
```

- **regression(input: number[])**  
  Computes the linear and polynomial regression from a set of data points.

```js
regression([
  [-2, -1],
  [1, 2],
  [4, 59],
  [-1, 4],
  [3, 24],
  [-4, -53]
]);

➔ {
  linear: {
    m: 10.97864768683274,
    b: 4.00355871886121
  },
  polynomial: {
    a: 6.689189189189188,
    b: 11.060810810810809,
    c: -0.34459459459459435
  }
}
```

### 📊 Population Statistics

- **populationDensity(population, area)**  
  Returns density (people per unit area).

- **birthRate(births, population)**  
  Returns births per 1000 people.

- **deathRate(deaths, population)**  
  Returns deaths per 1000 people.

- **Population Data**  
  Pre-defined population figures (as of Feb 2025):
  ```javascript
  population.br.sp; // Brazil São Paulo: 11,452,000
  population.us.ny; // USA New York: 20,201,249
  ```

## Contributing

Contributions are welcome! Please follow the [contribution guidelines](https://github.com/igorwastaken/math-utils/blob/main/CONTRIBUTING.md).

1. Clone the repository:
   ```bash
   git clone https://github.com/igorwastaken/math-utils.git
   ```
2. Install dependencies:
   ```bash
   npm install
   ```
3. Run tests:
   ```bash
   npm test
   ```

## License

MIT © Igor Figueiredo  
[Full License Text](LICENSE)