Partial Matrix

class fastmat.Partial

Bases: fastmat.Matrix.Matrix

Let \(I \subset \{1,\dots,n\}\) and \(J \subset \{1,\dots,m\}\) index sets and \(M \in \mathbb{C}^{n \times m}\) a linear transform. Then the partial transform \(M_{I,J}\) is defined as

\[x \in \mathbb{C}^m \mapsto ( M_J \cdot x_J)_{i \in I}.\]

In other words, we select the rows \(I\) of \(M\) and columns J of \(M\) and rows \(J\) of \(x\).

>>> # import the package
>>> import fastmat as fm
>>> import numpy as np
>>>
>>> # define the index set
>>> a = np.arange(n)
>>> am = np.mod(a, 2)
>>> b = np.array(am, dtype='bool')
>>> I = a[b]
>>>
>>> # construct the partial transform
>>> M = fm.Partial(F, I)

Let \({\mathcal{F}}\) be the \(n\)-dimensional Fourier matrix. And let \(I\) be the set of odd integers. Then we define a partial transform as

\[M = {\mathcal{F}}_I\]
__init__

Initialize a Partial matrix instance.

Parameters:
mat : fastmat.Matrix

A fastmat matrix instance subject to partial access.

rows : numpy.ndarray, optional

A 1d vector selecting rows of mat.

If N is of type bool it’s size must match the height of mat and the values of N corresponds to taking/dumping the corresponding row.

If N is of type int it’s values correspond to the indices of the rows of mat to select. The size of N then matches the height of the partialed matrix.

Defaults to selecting all rows.

cols : numpy.ndarray, optional

A 1d vector selecting columns of mat. The behaviour is identical to N.

Defaults to selecting all columns.

**options : optional

Additional optional keyworded arguments. Supports all optional arguments supported by fastmat.Matrix.

colSelection

Return the support of the base matrix which defines the partial

Subselected columns

(read only)

indicesM

Deprecated. See .colSelection

indicesN

Deprecated. See .rowSelection

rowSelection

Return the support of the base matrix which defines the partial

Subselected rows

(read only)