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Module « numpy.matlib »

Fonction polyval - module numpy.matlib

Signature de la fonction polyval

def polyval(p, x) 

Description

help(numpy.matlib.polyval)

Evaluate a polynomial at specific values.

.. note::
   This forms part of the old polynomial API. Since version 1.4, the
   new polynomial API defined in `numpy.polynomial` is preferred.
   A summary of the differences can be found in the
   :doc:`transition guide </reference/routines.polynomials>`.

If `p` is of length N, this function returns the value::

    p[0]*x**(N-1) + p[1]*x**(N-2) + ... + p[N-2]*x + p[N-1]

If `x` is a sequence, then ``p(x)`` is returned for each element of ``x``.
If `x` is another polynomial then the composite polynomial ``p(x(t))``
is returned.

Parameters
----------
p : array_like or poly1d object
   1D array of polynomial coefficients (including coefficients equal
   to zero) from highest degree to the constant term, or an
   instance of poly1d.
x : array_like or poly1d object
   A number, an array of numbers, or an instance of poly1d, at
   which to evaluate `p`.

Returns
-------
values : ndarray or poly1d
   If `x` is a poly1d instance, the result is the composition of the two
   polynomials, i.e., `x` is "substituted" in `p` and the simplified
   result is returned. In addition, the type of `x` - array_like or
   poly1d - governs the type of the output: `x` array_like => `values`
   array_like, `x` a poly1d object => `values` is also.

See Also
--------
poly1d: A polynomial class.

Notes
-----
Horner's scheme [1]_ is used to evaluate the polynomial. Even so,
for polynomials of high degree the values may be inaccurate due to
rounding errors. Use carefully.

If `x` is a subtype of `ndarray` the return value will be of the same type.

References
----------
.. [1] I. N. Bronshtein, K. A. Semendyayev, and K. A. Hirsch (Eng.
   trans. Ed.), *Handbook of Mathematics*, New York, Van Nostrand
   Reinhold Co., 1985, pg. 720.

Examples
--------
>>> import numpy as np
>>> np.polyval([3,0,1], 5)  # 3 * 5**2 + 0 * 5**1 + 1
76
>>> np.polyval([3,0,1], np.poly1d(5))
poly1d([76])
>>> np.polyval(np.poly1d([3,0,1]), 5)
76
>>> np.polyval(np.poly1d([3,0,1]), np.poly1d(5))
poly1d([76])

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