qmkpy.io module

Input/Output functions.

This module contains functions to save and load QMKP instances.

qmkpy.io.load_problem_json(fname: str)

Load a previously stored QMKProblem instance from the JSON format

This function allows loading a QMKProblem from a .json file, which was created by the qmkpy.io.save_problem_json() method.

See also

qmkpy.io.save_problem_json(): For saving a model in the JSON format.

Parameters: fname (str or PathLike) – Filepath of the saved model
Returns: problem – Loaded problem instance
Return type: qmkpy.QMKProblem

qmkpy.io.load_problem_numpy(fname: str)

Load a previously stored QMKProblem instance from the Numpy format

This function allows loading a QMKProblem from a compressed .npz file, which was created by the qmkpy.io.save_problem_numpy() method.

See also

qmkpy.io.save_problem_numpy(): For saving a model in the Numpy format.
numpy.load(): For details on loading the .npz format.

Parameters: fname (str or PathLike) – Filepath of the saved model
Returns: problem – Loaded problem instance
Return type: qmkpy.QMKProblem

qmkpy.io.load_problem_pickle(fname: Union[str, bytes, PathLike])

Load a previously stored QMKProblem instance from the Pickle format

This function allows loading a QMKProblem object from a Python pickled object file.

Caution: All warnings as for the regular pickle.load() apply!

See also

qmkpy.io.save_problem_pickle(): For saving a model in the Pickle format.
pickle.load(): For details on loading a pickled object.

Parameters: fname (str or PathLike) – Filepath of the saved model
Returns: problem – Loaded problem instance
Return type: qmkpy.QMKProblem

qmkpy.io.load_problem_txt(fname: Union[str, bytes, PathLike], sep: str = '\t')

Load a previously stored QMKProblem instance from the text format

This function loads a QMKProblem instance from a text file according to the format specified in qmkpy.io.save_problem_txt().

See also

qmkpy.io.save_problem_txt(): For saving a model in the text format.

Parameters

fname (str or PathLike) – Filepath of the saved model
sep (str) – Separator string that is used to separate the numbers in the file.

Returns

problem – Loaded problem instance

Return type

qmkpy.QMKProblem

qmkpy.io.save_problem_json(fname: Union[str, bytes, PathLike], problem, name: Optional[str] = None)

Save a QMKProblem as a JSON file

Save a QMKProblem instance using the JavaScript Object Notation (JSON) format. This only saves the problem.profits, problem.weights and problem.capacities arrays, and the problem.name attribute if it is set.

See also

load_problem_json(): For loading a saved model.

Parameters

fname (str or PathLike) – Filepath of the model to be saved at
problem (qmkpy.QMKProblem) – Problem instance to be saved
name (str ,optional) – Optional name of the problem that is used as the first line of the output file. If it is None, it will first be checked whether the attribute problem.name is set. If this is also None, the name defaults to qmkp_{num_items:d}_{num_ks:d}_{np.random.randint(0, 1000):03d}.

Return type

None

qmkpy.io.save_problem_numpy(fname: Union[str, bytes, PathLike], problem)

Save a QMKProblem using Numpys npz format

Save a QMKProblem instance using the compressed npz format. This only saves the problem.profits, problem.weights, and problem.capacities arrays.

See also

load_problem_numpy(): For loading a saved model.
numpy.savez_compressed(): For details on the .npz format.

Parameters

fname (str or PathLike) – Filepath of the model to be saved at
problem (qmkpy.QMKProblem) – Problem instance to be saved

Return type

None

qmkpy.io.save_problem_pickle(fname: Union[str, bytes, PathLike], problem)

Save a QMKProblem using the Python Pickle format

Save a QMKProblem object using the Python pickle library. By this, the whole object is stored in a binary format.

See also

qmkpy.io.load_problem_pickle(): For loading a saved model.
pickle.dump(): For details on the underlying pickling function.

Parameters

fname (str or PathLike) – Filepath of the model to be saved at
problem (qmkpy.QMKProblem) – Problem instance to be saved

Return type

None

qmkpy.io.save_problem_txt(fname: Union[str, bytes, PathLike], qmkp, sep: str = '\t', name: Optional[str] = None)

Save a QMKProblem instance in text form

Save a QMKProblem instance in text form inspired by the format established by Alain Billionnet and Eric Soutif for the regular QKP. The original description can be found at https://cedric.cnam.fr/~soutif/QKP/format.html.

The file format is as follows:

The first line provides a name/reference of the problem

The second line specifies the number of items

The third line specifies the number of knapsacks

The fourth line is blank to separate the meta information from the rest

The fifth line contains the linear profits (main diagonal elements of the profit matrix) separated by sep.

The next lines contain the upper triangular part of the profit matrix (i.e., \(p_{ij}\)).

Blank line separating profits from the rest

Weights \(w_{i}\) of the items, separated by sep.

Blank line separating weights and capacities

Capacities \(c_{u}\) of the knapsacks, separated by sep.

For the example with parameters

\[\begin{split}P = \begin{pmatrix}1 & 2 & 3\\ 2 & 4 & 5\\ 3 & 5 & 6\end{pmatrix}, \quad w = \begin{pmatrix}10\\ 20\\ 30\end{pmatrix}, \quad c = \begin{pmatrix}5 \\ 8\\ 1\\ 9\\ 2\end{pmatrix}\end{split}\]

the output-file looks as follows

Name of the Problem
3
5

1   4   6
2   3
5

10  20  30

5   8   1   9   2

See also

qmkpy.io.load_problem_txt(): For loading a saved model.

Parameters

fname (str or PathLike) – Filepath of the model to be saved at
problem (qmkpy.QMKProblem) – Problem instance to be saved
sep (str) – Separator string that is used to separate the numbers in the file.
name (str ,optional) – Optional name of the problem that is used as the first line of the output file. If it is None, it will first be checked whether the attribute problem.name is set. If this is also None, the name defaults to qmkp_{num_items:d}_{num_ks:d}_{np.random.randint(0, 1000):03d}.

Return type

None