Merge branch 'develop'

Author: paolodragone

MANIFEST.in

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+include LICENSE

README.md

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-# Pyconstruct
-A Python library for declarative, constrained, structured-output prediction.
+Pyconstruct
+===========
 
-## Coming soon
+<div align="center">
+  <img height="300px" src="docs/_static/images/pyconstruct.png"><br><br>
+</div>
+
+**Pyconstruct** is a Python library for declarative, constrained,
+structured-output prediction. When using Pyconstruct, the problem specification
+can be encoded in MiniZinc, a high-level constraint programming language. This
+means that domain knowledge can be declaratively included in the inference
+procedure as constraints over the optimization variables.
+
+Sounds complicated? A simple example will clear up the doubts!
+
+
+Getting started
+---------------
+
+In the following example we will implement a simple OCR (Optical Character
+Recognition) model in few lines of MiniZinc.
+
+First of all, lets fetch the data. Pyconstruct has a utility for getting some
+standard datasets::
+
+```python
+    from pyconstruct import datasets
+    ocr = datasets.load('ocr')
+```
+
+The first time the dataset is loaded it will actually be fetched from the web
+and stored locally. You can now see the description of the dataset::
+
+```python
+    print(ocr.descr)
+```
+
+By default, structured objects are represented as Python dictionaries in
+Pyconstruct. Each objects as several "attributes", identified with some string.
+Each attribute value may be any basic Python data type: strings, integers,
+floats, list or other dictionaries. In OCR, for instance, inputs `X` are
+represented as dictionaries containing two attributes: an integer containing the
+`length` of the word; a list of `16x8` matrices (`numpy.ndarray`) containing the
+bitmap images of each character in the word. The targets (labels) are also
+structured objects containig a single attribute `sequence`, a list of integers
+representing the letters associated to each image in the word. For instance::
+
+```python
+    print(ocr.data[0])
+    print(ocr.targets[0])
+```
+
+After getting the data, we can start coding our problem. First of all, in
+Pyconstruct there are three main kinds of objects to interact with: Domains,
+Models and Learners. At a high level: a Domain defines the attributes and the
+constraints of the structured objects; a Model is an object contaning some
+parameters that can be used to make inference over a Domain; a Learner is an
+algorithm that can learn a Model from data. A Domain is also responsible of
+solving inference problems with respect to some Model, so the two classes are
+interdependent, but in general a Domain can be made working for different
+Models.
+
+Several Models and Learners are already defined by Pyconstruct. All that is
+required for start training a model, apart from the data, is a Domain encoded in
+MiniZinc which defines how the attributes of the objects interact, which are the
+constraints and the features of the objects. To do so, we need to create a
+`ocr.pmzn` file::
+
+```HTML+Django
+    {% from 'pyconstruct.pmzn' import n_features, features, domain, solve %}
+
+    {{ n_features('16 * 8 * 26') }}
+
+    {% call domain(problem) %}
+
+        int: length;
+        array[1 .. length, 1 .. 16, 1 .. 8] of var {0, 1}: images;
+
+        array[1 .. length] of var 1 .. 26: sequence;
+
+
+        {% call features(feature_type='int') %}
+        [
+            sum(e in 1 .. length)(images[e, i, j] * (sequence[e] == s))
+            | i in 1 .. 16, j in 1 .. 8, s in 1 .. 26
+        ]
+        {% endcall %}
+
+    {% endcall %}
+
+    {{ solve(problem, model, discretize=True) }}
+```
+
+That's it! Now we can instantiate a `Domain` with our new `ocr.pmzn` file::
+
+```python
+    from pyconstruct import Domain
+    ocr_dom = Domain('ocr.pmzn')
+```
+
+If you know MiniZinc, the above code will probably look a bit odd. That is
+because Pyconstruct by default uses a superset of MiniZinc defined by the PyMzn
+library.  Essentially, that is MiniZinc with some tempating provided by the
+Jinja2 library. Check out PyMzn for an explanation on how to use fully it. Here
+we'll explain the basics.
+
+The first line
+`{% from 'pyconstruct.pmzn' import n_features, features, domain, solve %}`
+imports few useful macros from the `pyconstruct.pmzn` file.
+
+The second line `{{ n_features('16 * 8 * 26') }}` calls the `n_features` macro,
+which compiles into::
+
+```HTML+Django
+    int: N_FEATURES = 16 * 8 * 26;
+    set of int: FEATURES 1 .. N_FEATURES;
+```
+
+The MiniZinc code enclosed in the tags
+`{% call domain(problem) %} ... {% endcall %}` is processed on the basis of the
+value of `problem` the domain is called with. The variable `problem` is usually
+passed to the domain by an internal call of Pyconstruct through PyMzn. In this
+block goes the domain definition, including the variables and parameters of the
+objects, the constraints and the features. Notice that we have two MiniZinc
+parameters `length` and `images`, which match the attributes of the input
+objects of the OCR dataset, and one optimization variable `sequence` which
+matches the attribute of the output objects of the OCR dataset. This is valid
+for any problem: the examples are the inputs that are provided as dzn data,
+whereas the targets are the outputs of the model, which translate into
+optimization variables when solving inference.
+
+Inside the domain call we also call the `features` macro, which compiles into::
+
+```HTML+Django
+    array[FEATURES] of var int: phi = [
+        sum(e in 1 .. length)(images[e, i, j] * (sequence[e] == s))
+        | i in 1 .. 16, j in 1 .. 8, s in 1 .. 26
+    ];
+```
+
+These are typical features used in OCR, for each symbol `s` and each pixel `(i,
+j)` in the images containing the number of times in the sequence the `(i, j)`
+pixel is active for characters labeled with symbol `s`.
+
+The last line calls the `solve` macro, which compiles to a different solve
+statement depending on the `problem` and `model`. Possible values for `problem`
+are, for instance, `map` to find the object with highest score (dot product
+between weights and features) or `phi` to compute the feature vector given an
+input and an output object. The `model` is a dictionary containing the model's
+parameters, such as the weights `w` for a `LinearModel`. Also this object is
+usually passed to the domain by Pyconstruct.
+
+The above model is actually a partial example of the complete `ocr` domain
+available in Pyconstruct out-of-the-box. You can load the domain by simply::
+
+```python
+    ocr_dom = Domain('ocr')
+```
+
+After defining the domain, using the predefined one or the `ocr.pmzn` file, we
+can start learning by instantiating a learner, say a `StructuredPerceptron`, and
+fitting the data::
+
+```python
+    from pyconstruct import StructuredPerceptron
+    sp = StructuredPerceptron(domain=ocr_dom)
+    sp.fit(ocr.data, ocr.targets)
+```
+
+This will take a while... If you need a quick benchmark, Pyconstruct contains
+pretrained models for many domains and learners (link).
+
+
+Install
+-------
+Pyconstruct can be installed through `pip`:
+
+```bash
+pip install pyconstruct
+```
+
+Or by downloading the code from Github and running the following from the
+downloaded directory:
+
+```bash
+python setup.py install
+```
+
+After installing Pyconstruct you will need to install **MiniZinc** as well.
+Download the latest release of MiniZincIDE and follow the instructions.
+
+Authors
+-------
+This project is developed at the SML research group at the University of Trento
+(Italy). Main developers and maintainers:
+
+* Paolo Dragone
+* Stefano Teso (now at KU Leuven)
+* Andrea Passerini
 

docs/.buildinfo

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