# Getting started¶

`scikit-network`

is an open-source python package for the analysis of large graphs.

## Installation¶

Install `scikit-network`

:

```
$ pip install scikit-network
```

Import `scikit-network`

in a Python project:

```
import sknetwork as skn
```

## Data format¶

Each graph is represented by its adjacency matrix, either as a dense `numpy array`

or a sparse `scipy CSR matrix`

.
A bipartite graph can be represented by its biadjacency matrix, in the same format.

## Documentation¶

We use the following notations in the documentation:

### Graphs¶

For undirected graphs:

\(A\) is the adjacency matrix of the graph (dimension \(n\times n\))

\(d = A1\) is the vector of node weights (node degrees if the matrix \(A\) is binary)

\(D = \text{diag}(d)\) the diagonal matrix of node weights

### Digraphs¶

For directed graphs:

\(A\) is the adjacency matrix of the graph (dimension \(n\times n\))

\(d^+ = A1\) and \(d^- = A^T1\) are the vectors of out-weights and in-weights of nodes (out-degrees and in-degrees if the matrix \(A\) is binary)

\(D^+ = \text{diag}(d^+)\) and \(D^- = \text{diag}(d^-)\) are the diagonal matrices of out-weights and in-weights

### Bigraphs¶

For bipartite graphs:

\(B\) is the biadjacency matrix of the graph (dimension \(n_1\times n_2\))

\(d_1 = B1\) and \(d_2 = B^T1\) are the vectors of weights (rows and columns)

\(D_1 = \text{diag}(d_1)\) and \(D_2 = \text{diag}(d_2)\) are the diagonal matrices of weights.

### Notes¶

Adjacency and biadjacency matrices have non-negative entries (the weights of the edges).

Bipartite graphs are undirected but have a special structure that is exploited by some algorithms. These algorithms are identified with the prefix

`Bi`

.