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"""
Utility classes and functions for the polynomial modules.
This module provides: error and warning objects; a polynomial base class;
and some routines used in both the `polynomial` and `chebyshev` modules.
Error objects
-------------
.. autosummary::
:toctree: generated/
PolyError base class for this sub-package's errors.
PolyDomainError raised when domains are mismatched.
Warning objects
---------------
.. autosummary::
:toctree: generated/
RankWarning raised in least-squares fit for rank-deficient matrix.
Base class
----------
.. autosummary::
:toctree: generated/
PolyBase Obsolete base class for the polynomial classes. Do not use.
Functions
---------
.. autosummary::
:toctree: generated/
as_series convert list of array_likes into 1-D arrays of common type.
trimseq remove trailing zeros.
trimcoef remove small trailing coefficients.
getdomain return the domain appropriate for a given set of abscissae.
mapdomain maps points between domains.
mapparms parameters of the linear map between domains.
"""
from __future__ import division, absolute_import, print_function
import numpy as np
__all__ = [
'RankWarning', 'PolyError', 'PolyDomainError', 'as_series', 'trimseq',
'trimcoef', 'getdomain', 'mapdomain', 'mapparms', 'PolyBase']
#
# Warnings and Exceptions
#
class RankWarning(UserWarning):
"""Issued by chebfit when the design matrix is rank deficient."""
pass
class PolyError(Exception):
"""Base class for errors in this module."""
pass
class PolyDomainError(PolyError):
"""Issued by the generic Poly class when two domains don't match.
This is raised when an binary operation is passed Poly objects with
different domains.
"""
pass
#
# Base class for all polynomial types
#
class PolyBase(object):
"""
Base class for all polynomial types.
Deprecated in numpy 1.9.0, use the abstract
ABCPolyBase class instead. Note that the latter
requires a number of virtual functions to be
implemented.
"""
pass
#
# Helper functions to convert inputs to 1-D arrays
#
def trimseq(seq):
"""Remove small Poly series coefficients.
Parameters
----------
seq : sequence
Sequence of Poly series coefficients. This routine fails for
empty sequences.
Returns
-------
series : sequence
Subsequence with trailing zeros removed. If the resulting sequence
would be empty, return the first element. The returned sequence may
or may not be a view.
Notes
-----
Do not lose the type info if the sequence contains unknown objects.
"""
if len(seq) == 0:
return seq
else:
for i in range(len(seq) - 1, -1, -1):
if seq[i] != 0:
break
return seq[:i+1]
def as_series(alist, trim=True):
"""
Return argument as a list of 1-d arrays.
The returned list contains array(s) of dtype double, complex double, or
object. A 1-d argument of shape ``(N,)`` is parsed into ``N`` arrays of
size one; a 2-d argument of shape ``(M,N)`` is parsed into ``M`` arrays
of size ``N`` (i.e., is "parsed by row"); and a higher dimensional array
raises a Value Error if it is not first reshaped into either a 1-d or 2-d
array.
Parameters
----------
alist : array_like
A 1- or 2-d array_like
trim : boolean, optional
When True, trailing zeros are removed from the inputs.
When False, the inputs are passed through intact.
Returns
-------
[a1, a2,...] : list of 1-D arrays
A copy of the input data as a list of 1-d arrays.
Raises
------
ValueError
Raised when `as_series` cannot convert its input to 1-d arrays, or at
least one of the resulting arrays is empty.
Examples
--------
>>> from numpy import polynomial as P
>>> a = np.arange(4)
>>> P.as_series(a)
[array([ 0.]), array([ 1.]), array([ 2.]), array([ 3.])]
>>> b = np.arange(6).reshape((2,3))
>>> P.as_series(b)
[array([ 0., 1., 2.]), array([ 3., 4., 5.])]
"""
arrays = [np.array(a, ndmin=1, copy=0) for a in alist]
if min([a.size for a in arrays]) == 0:
raise ValueError("Coefficient array is empty")
if any([a.ndim != 1 for a in arrays]):
raise ValueError("Coefficient array is not 1-d")
if trim:
arrays = [trimseq(a) for a in arrays]
if any([a.dtype == np.dtype(object) for a in arrays]):
ret = []
for a in arrays:
if a.dtype != np.dtype(object):
tmp = np.empty(len(a), dtype=np.dtype(object))
tmp[:] = a[:]
ret.append(tmp)
else:
ret.append(a.copy())
else:
try:
dtype = np.common_type(*arrays)
except:
raise ValueError("Coefficient arrays have no common type")
ret = [np.array(a, copy=1, dtype=dtype) for a in arrays]
return ret
def trimcoef(c, tol=0):
"""
Remove "small" "trailing" coefficients from a polynomial.
"Small" means "small in absolute value" and is controlled by the
parameter `tol`; "trailing" means highest order coefficient(s), e.g., in
``[0, 1, 1, 0, 0]`` (which represents ``0 + x + x**2 + 0*x**3 + 0*x**4``)
both the 3-rd and 4-th order coefficients would be "trimmed."
Parameters
----------
c : array_like
1-d array of coefficients, ordered from lowest order to highest.
tol : number, optional
Trailing (i.e., highest order) elements with absolute value less
than or equal to `tol` (default value is zero) are removed.
Returns
-------
trimmed : ndarray
1-d array with trailing zeros removed. If the resulting series
would be empty, a series containing a single zero is returned.
Raises
------
ValueError
If `tol` < 0
See Also
--------
trimseq
Examples
--------
>>> from numpy import polynomial as P
>>> P.trimcoef((0,0,3,0,5,0,0))
array([ 0., 0., 3., 0., 5.])
>>> P.trimcoef((0,0,1e-3,0,1e-5,0,0),1e-3) # item == tol is trimmed
array([ 0.])
>>> i = complex(0,1) # works for complex
>>> P.trimcoef((3e-4,1e-3*(1-i),5e-4,2e-5*(1+i)), 1e-3)
array([ 0.0003+0.j , 0.0010-0.001j])
"""
if tol < 0:
raise ValueError("tol must be non-negative")
[c] = as_series([c])
[ind] = np.where(np.abs(c) > tol)
if len(ind) == 0:
return c[:1]*0
else:
return c[:ind[-1] + 1].copy()
def getdomain(x):
"""
Return a domain suitable for given abscissae.
Find a domain suitable for a polynomial or Chebyshev series
defined at the values supplied.
Parameters
----------
x : array_like
1-d array of abscissae whose domain will be determined.
Returns
-------
domain : ndarray
1-d array containing two values. If the inputs are complex, then
the two returned points are the lower left and upper right corners
of the smallest rectangle (aligned with the axes) in the complex
plane containing the points `x`. If the inputs are real, then the
two points are the ends of the smallest interval containing the
points `x`.
See Also
--------
mapparms, mapdomain
Examples
--------
>>> from numpy.polynomial import polyutils as pu
>>> points = np.arange(4)**2 - 5; points
array([-5, -4, -1, 4])
>>> pu.getdomain(points)
array([-5., 4.])
>>> c = np.exp(complex(0,1)*np.pi*np.arange(12)/6) # unit circle
>>> pu.getdomain(c)
array([-1.-1.j, 1.+1.j])
"""
[x] = as_series([x], trim=False)
if x.dtype.char in np.typecodes['Complex']:
rmin, rmax = x.real.min(), x.real.max()
imin, imax = x.imag.min(), x.imag.max()
return np.array((complex(rmin, imin), complex(rmax, imax)))
else:
return np.array((x.min(), x.max()))
def mapparms(old, new):
"""
Linear map parameters between domains.
Return the parameters of the linear map ``offset + scale*x`` that maps
`old` to `new` such that ``old[i] -> new[i]``, ``i = 0, 1``.
Parameters
----------
old, new : array_like
Domains. Each domain must (successfully) convert to a 1-d array
containing precisely two values.
Returns
-------
offset, scale : scalars
The map ``L(x) = offset + scale*x`` maps the first domain to the
second.
See Also
--------
getdomain, mapdomain
Notes
-----
Also works for complex numbers, and thus can be used to calculate the
parameters required to map any line in the complex plane to any other
line therein.
Examples
--------
>>> from numpy import polynomial as P
>>> P.mapparms((-1,1),(-1,1))
(0.0, 1.0)
>>> P.mapparms((1,-1),(-1,1))
(0.0, -1.0)
>>> i = complex(0,1)
>>> P.mapparms((-i,-1),(1,i))
((1+1j), (1+0j))
"""
oldlen = old[1] - old[0]
newlen = new[1] - new[0]
off = (old[1]*new[0] - old[0]*new[1])/oldlen
scl = newlen/oldlen
return off, scl
def mapdomain(x, old, new):
"""
Apply linear map to input points.
The linear map ``offset + scale*x`` that maps the domain `old` to
the domain `new` is applied to the points `x`.
Parameters
----------
x : array_like
Points to be mapped. If `x` is a subtype of ndarray the subtype
will be preserved.
old, new : array_like
The two domains that determine the map. Each must (successfully)
convert to 1-d arrays containing precisely two values.
Returns
-------
x_out : ndarray
Array of points of the same shape as `x`, after application of the
linear map between the two domains.
See Also
--------
getdomain, mapparms
Notes
-----
Effectively, this implements:
.. math ::
x\\_out = new[0] + m(x - old[0])
where
.. math ::
m = \\frac{new[1]-new[0]}{old[1]-old[0]}
Examples
--------
>>> from numpy import polynomial as P
>>> old_domain = (-1,1)
>>> new_domain = (0,2*np.pi)
>>> x = np.linspace(-1,1,6); x
array([-1. , -0.6, -0.2, 0.2, 0.6, 1. ])
>>> x_out = P.mapdomain(x, old_domain, new_domain); x_out
array([ 0. , 1.25663706, 2.51327412, 3.76991118, 5.02654825,
6.28318531])
>>> x - P.mapdomain(x_out, new_domain, old_domain)
array([ 0., 0., 0., 0., 0., 0.])
Also works for complex numbers (and thus can be used to map any line in
the complex plane to any other line therein).
>>> i = complex(0,1)
>>> old = (-1 - i, 1 + i)
>>> new = (-1 + i, 1 - i)
>>> z = np.linspace(old[0], old[1], 6); z
array([-1.0-1.j , -0.6-0.6j, -0.2-0.2j, 0.2+0.2j, 0.6+0.6j, 1.0+1.j ])
>>> new_z = P.mapdomain(z, old, new); new_z
array([-1.0+1.j , -0.6+0.6j, -0.2+0.2j, 0.2-0.2j, 0.6-0.6j, 1.0-1.j ])
"""
x = np.asanyarray(x)
off, scl = mapparms(old, new)
return off + scl*x
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