Knee or elbow detection for curves

# kneebow

Find the knee of a curve or the elbow of a curve.

## How it works

kneebow builds upon a very simple idea: if we want to find the elbow of a curve, we can simply rotate the data so that curve looks down and then take the minimum value. If we want to find the knee of the curve, we take the maximum value instead. It's as simple as that.

## Installation

You can install the package via pip:

```pip install kneebow
```

```pip install git+https://github.com/georg-un/kneebow.git
```

## Usage

Let's assume, we try to find the elbow of the following data:

```import numpy as np
data = np.array([[1, 1], [2, 2], [3, 3], [4, 4], [5, 5], [6, 6], [7, 7], [8, 8],  # linear until (8,8)
[9, 16], [10, 32], [11, 64], [12, 128], [13, 256], [14, 512]])   # exponential afterwards
```

Let's have a peak how this data looks like:

To find the elbow, we create an instance of the `Rotor` class and use its `fit_rotate` method:

```from kneebow.rotor import Rotor

rotor = Rotor()
rotor.fit_rotate(data)
```

Now we can get the index of the elbow as follows:

```elbow_idx = rotor.get_elbow_index()
print(elbow_idx)  # 11
```

The `Rotor` class also comes with plot methods to inspect the data visually together with the estimated elbow/knee:

```rotor.plot_elbow()
```

Distributed under the MIT License. See `LICENSE` for more information.