# Get Started

## Basic Install by pip

You can install the stable release on PyPI:

```
$ pip install pygmtools
```

or get the latest version by running:

```
$ pip install -U https://github.com/Thinklab-SJTU/pygmtools/archive/master.zip # with --user for user install (no root)
```

Now the pygmtools is available with the `numpy`

backend:

You may jump to Example: Matching Isomorphic Graphs if you do not need other backends.

The following packages are required, and shall be automatically installed by `pip`

:

```
Python >= 3.5
requests >= 2.25.1
scipy >= 1.4.1
Pillow >= 7.2.0
numpy >= 1.18.5
easydict >= 1.7
appdirs >= 1.4.4
tqdm >= 4.64.1
```

## Install Other Backends

Currently, we also support deep learning architectures `pytorch`

, `paddle`

, `jittor`

which are GPU-friendly and deep learning-friendly.

Once the backend is ready, you may switch to the backend globally by the following command:

```
>>> import pygmtools as pygm
>>> pygm.BACKEND = 'pytorch' # replace 'pytorch' by other backend names
```

### PyTorch Backend

PyTorch is an open-source machine learning framework developed and maintained by Meta Inc./Linux Foundation.
PyTorch is popular, especially among the deep learning research community.
The PyTorch backend of `pygmtools`

is designed to support GPU devices and facilitate deep learning research.

Please follow the official PyTorch installation guide.

This package is developed with `torch==1.6.0`

and shall work with any PyTorch versions `>=1.6.0`

.

How to enable PyTorch backend:

```
>>> import pygmtools as pygm
>>> import torch
>>> pygm.BACKEND = 'pytorch'
```

### Paddle Backend

PaddlePaddle is an open-source deep learning platform originated from industrial practice, which is developed and
maintained by Baidu Inc.
The Paddle backend of `pygmtools`

is designed to support GPU devices and deep learning applications.

Please follow the official PaddlePaddle installation guide.

This package is developed with `paddlepaddle==2.3.1`

and shall work with any PaddlePaddle versions `>=2.3.1`

.

How to enable Paddle backend:

```
>>> import pygmtools as pygm
>>> import paddle
>>> pygm.BACKEND = 'paddle'
```

### Jittor Backend

Jittor is an open-source deep learning platform based on just-in-time (JIT) for high performance, which is developed
and maintained by the CSCG group from Tsinghua University.
The Jittor backend of `pygmtools`

is designed to support GPU devices and deep learning applications.

Please follow the official Jittor installation guide.

This package is developed with `jittor==1.3.4.16`

and shall work with any Jittor versions `>=1.3.4.16`

.

How to enable Jittor backend:

```
>>> import pygmtools as pygm
>>> import jittor
>>> pygm.BACKEND = 'jittor'
```

## Example: Matching Isomorphic Graphs

Here we provide a basic example of matching two isomorphic graphs (i.e. two graphs have the same nodes and edges, but the node permutations are unknown).

Step 0: Import packages and set backend

```
>>> import numpy as np
>>> import pygmtools as pygm
>>> pygm.BACKEND = 'numpy'
>>> np.random.seed(1)
```

Step 1: Generate a batch of isomorphic graphs

```
>>> batch_size = 3
>>> X_gt = np.zeros((batch_size, 4, 4))
>>> X_gt[:, np.arange(0, 4, dtype=np.int64), np.random.permutation(4)] = 1
>>> A1 = np.random.rand(batch_size, 4, 4)
>>> A2 = np.matmul(np.matmul(X_gt.transpose((0, 2, 1)), A1), X_gt)
>>> n1 = n2 = np.repeat([4], batch_size)
```

Step 2: Build an affinity matrix and select an affinity function

```
>>> conn1, edge1, ne1 = pygm.utils.dense_to_sparse(A1)
>>> conn2, edge2, ne2 = pygm.utils.dense_to_sparse(A2)
>>> import functools
>>> gaussian_aff = functools.partial(pygm.utils.gaussian_aff_fn, sigma=1.) # set affinity function
>>> K = pygm.utils.build_aff_mat(None, edge1, conn1, None, edge2, conn2, n1, ne1, n2, ne2, edge_aff_fn=gaussian_aff)
```

Step 3: Solve graph matching by RRWM

```
>>> X = pygm.rrwm(K, n1, n2, beta=100)
>>> X = pygm.hungarian(X)
>>> X # X is the permutation matrix
[[[0. 0. 0. 1.]
[0. 0. 1. 0.]
[1. 0. 0. 0.]
[0. 1. 0. 0.]]
[[0. 0. 0. 1.]
[0. 0. 1. 0.]
[1. 0. 0. 0.]
[0. 1. 0. 0.]]
[[0. 0. 0. 1.]
[0. 0. 1. 0.]
[1. 0. 0. 0.]
[0. 1. 0. 0.]]]
```

Final Step: Evaluate the accuracy

```
>>> (X * X_gt).sum() / X_gt.sum()
1.0
```

## What’s Next

Please checkout Examples Gallery to see how to apply `pygmtools`

to tackle real-world problems.
You may see API and Modules for the API documentation.