Fixed database typo and removed unnecessary class identifier.

venv/Lib/site-packages/scipy/sparse/linalg/_norm.py

@@ -0,0 +1,182 @@
+"""Sparse matrix norms.
+
+"""
+import numpy as np
+from scipy.sparse import issparse
+
+from numpy import Inf, sqrt, abs
+
+__all__ = ['norm']
+
+
+def _sparse_frobenius_norm(x):
+    if np.issubdtype(x.dtype, np.complexfloating):
+        sqnorm = abs(x).power(2).sum()
+    else:
+        sqnorm = x.power(2).sum()
+    return sqrt(sqnorm)
+
+
+def norm(x, ord=None, axis=None):
+    """
+    Norm of a sparse matrix
+
+    This function is able to return one of seven different matrix norms,
+    depending on the value of the ``ord`` parameter.
+
+    Parameters
+    ----------
+    x : a sparse matrix
+        Input sparse matrix.
+    ord : {non-zero int, inf, -inf, 'fro'}, optional
+        Order of the norm (see table under ``Notes``). inf means numpy's
+        `inf` object.
+    axis : {int, 2-tuple of ints, None}, optional
+        If `axis` is an integer, it specifies the axis of `x` along which to
+        compute the vector norms.  If `axis` is a 2-tuple, it specifies the
+        axes that hold 2-D matrices, and the matrix norms of these matrices
+        are computed.  If `axis` is None then either a vector norm (when `x`
+        is 1-D) or a matrix norm (when `x` is 2-D) is returned.
+
+    Returns
+    -------
+    n : float or ndarray
+
+    Notes
+    -----
+    Some of the ord are not implemented because some associated functions like,
+    _multi_svd_norm, are not yet available for sparse matrix.
+
+    This docstring is modified based on numpy.linalg.norm.
+    https://github.com/numpy/numpy/blob/master/numpy/linalg/linalg.py
+
+    The following norms can be calculated:
+
+    =====  ============================
+    ord    norm for sparse matrices
+    =====  ============================
+    None   Frobenius norm
+    'fro'  Frobenius norm
+    inf    max(sum(abs(x), axis=1))
+    -inf   min(sum(abs(x), axis=1))
+    0      abs(x).sum(axis=axis)
+    1      max(sum(abs(x), axis=0))
+    -1     min(sum(abs(x), axis=0))
+    2      Not implemented
+    -2     Not implemented
+    other  Not implemented
+    =====  ============================
+
+    The Frobenius norm is given by [1]_:
+
+        :math:`||A||_F = [\\sum_{i,j} abs(a_{i,j})^2]^{1/2}`
+
+    References
+    ----------
+    .. [1] G. H. Golub and C. F. Van Loan, *Matrix Computations*,
+        Baltimore, MD, Johns Hopkins University Press, 1985, pg. 15
+
+    Examples
+    --------
+    >>> from scipy.sparse import *
+    >>> import numpy as np
+    >>> from scipy.sparse.linalg import norm
+    >>> a = np.arange(9) - 4
+    >>> a
+    array([-4, -3, -2, -1, 0, 1, 2, 3, 4])
+    >>> b = a.reshape((3, 3))
+    >>> b
+    array([[-4, -3, -2],
+           [-1, 0, 1],
+           [ 2, 3, 4]])
+
+    >>> b = csr_matrix(b)
+    >>> norm(b)
+    7.745966692414834
+    >>> norm(b, 'fro')
+    7.745966692414834
+    >>> norm(b, np.inf)
+    9
+    >>> norm(b, -np.inf)
+    2
+    >>> norm(b, 1)
+    7
+    >>> norm(b, -1)
+    6
+
+    """
+    if not issparse(x):
+        raise TypeError("input is not sparse. use numpy.linalg.norm")
+
+    # Check the default case first and handle it immediately.
+    if axis is None and ord in (None, 'fro', 'f'):
+        return _sparse_frobenius_norm(x)
+
+    # Some norms require functions that are not implemented for all types.
+    x = x.tocsr()
+
+    if axis is None:
+        axis = (0, 1)
+    elif not isinstance(axis, tuple):
+        msg = "'axis' must be None, an integer or a tuple of integers"
+        try:
+            int_axis = int(axis)
+        except TypeError:
+            raise TypeError(msg)
+        if axis != int_axis:
+            raise TypeError(msg)
+        axis = (int_axis,)
+
+    nd = 2
+    if len(axis) == 2:
+        row_axis, col_axis = axis
+        if not (-nd <= row_axis < nd and -nd <= col_axis < nd):
+            raise ValueError('Invalid axis %r for an array with shape %r' %
+                             (axis, x.shape))
+        if row_axis % nd == col_axis % nd:
+            raise ValueError('Duplicate axes given.')
+        if ord == 2:
+            raise NotImplementedError
+            #return _multi_svd_norm(x, row_axis, col_axis, amax)
+        elif ord == -2:
+            raise NotImplementedError
+            #return _multi_svd_norm(x, row_axis, col_axis, amin)
+        elif ord == 1:
+            return abs(x).sum(axis=row_axis).max(axis=col_axis)[0,0]
+        elif ord == Inf:
+            return abs(x).sum(axis=col_axis).max(axis=row_axis)[0,0]
+        elif ord == -1:
+            return abs(x).sum(axis=row_axis).min(axis=col_axis)[0,0]
+        elif ord == -Inf:
+            return abs(x).sum(axis=col_axis).min(axis=row_axis)[0,0]
+        elif ord in (None, 'f', 'fro'):
+            # The axis order does not matter for this norm.
+            return _sparse_frobenius_norm(x)
+        else:
+            raise ValueError("Invalid norm order for matrices.")
+    elif len(axis) == 1:
+        a, = axis
+        if not (-nd <= a < nd):
+            raise ValueError('Invalid axis %r for an array with shape %r' %
+                             (axis, x.shape))
+        if ord == Inf:
+            M = abs(x).max(axis=a)
+        elif ord == -Inf:
+            M = abs(x).min(axis=a)
+        elif ord == 0:
+            # Zero norm
+            M = (x != 0).sum(axis=a)
+        elif ord == 1:
+            # special case for speedup
+            M = abs(x).sum(axis=a)
+        elif ord in (2, None):
+            M = sqrt(abs(x).power(2).sum(axis=a))
+        else:
+            try:
+                ord + 1
+            except TypeError:
+                raise ValueError('Invalid norm order for vectors.')
+            M = np.power(abs(x).power(ord).sum(axis=a), 1 / ord)
+        return M.A.ravel()
+    else:
+        raise ValueError("Improper number of dimensions to norm.")