Module « scipy.signal »

Fonction savgol_filter - module scipy.signal

Signature de la fonction savgol_filter

def savgol_filter(x, window_length, polyorder, deriv=0, delta=1.0, axis=-1, mode='interp', cval=0.0) 

Description

savgol_filter.__doc__

 Apply a Savitzky-Golay filter to an array.

    This is a 1-D filter. If `x`  has dimension greater than 1, `axis`
    determines the axis along which the filter is applied.

    Parameters
    ----------
    x : array_like
        The data to be filtered. If `x` is not a single or double precision
        floating point array, it will be converted to type ``numpy.float64``
        before filtering.
    window_length : int
        The length of the filter window (i.e., the number of coefficients).
        `window_length` must be a positive odd integer. If `mode` is 'interp',
        `window_length` must be less than or equal to the size of `x`.
    polyorder : int
        The order of the polynomial used to fit the samples.
        `polyorder` must be less than `window_length`.
    deriv : int, optional
        The order of the derivative to compute. This must be a
        nonnegative integer. The default is 0, which means to filter
        the data without differentiating.
    delta : float, optional
        The spacing of the samples to which the filter will be applied.
        This is only used if deriv > 0. Default is 1.0.
    axis : int, optional
        The axis of the array `x` along which the filter is to be applied.
        Default is -1.
    mode : str, optional
        Must be 'mirror', 'constant', 'nearest', 'wrap' or 'interp'. This
        determines the type of extension to use for the padded signal to
        which the filter is applied.  When `mode` is 'constant', the padding
        value is given by `cval`.  See the Notes for more details on 'mirror',
        'constant', 'wrap', and 'nearest'.
        When the 'interp' mode is selected (the default), no extension
        is used.  Instead, a degree `polyorder` polynomial is fit to the
        last `window_length` values of the edges, and this polynomial is
        used to evaluate the last `window_length // 2` output values.
    cval : scalar, optional
        Value to fill past the edges of the input if `mode` is 'constant'.
        Default is 0.0.

    Returns
    -------
    y : ndarray, same shape as `x`
        The filtered data.

    See Also
    --------
    savgol_coeffs

    Notes
    -----
    Details on the `mode` options:

        'mirror':
            Repeats the values at the edges in reverse order. The value
            closest to the edge is not included.
        'nearest':
            The extension contains the nearest input value.
        'constant':
            The extension contains the value given by the `cval` argument.
        'wrap':
            The extension contains the values from the other end of the array.

    For example, if the input is [1, 2, 3, 4, 5, 6, 7, 8], and
    `window_length` is 7, the following shows the extended data for
    the various `mode` options (assuming `cval` is 0)::

        mode       |   Ext   |         Input          |   Ext
        -----------+---------+------------------------+---------
        'mirror'   | 4  3  2 | 1  2  3  4  5  6  7  8 | 7  6  5
        'nearest'  | 1  1  1 | 1  2  3  4  5  6  7  8 | 8  8  8
        'constant' | 0  0  0 | 1  2  3  4  5  6  7  8 | 0  0  0
        'wrap'     | 6  7  8 | 1  2  3  4  5  6  7  8 | 1  2  3

    .. versionadded:: 0.14.0

    Examples
    --------
    >>> from scipy.signal import savgol_filter
    >>> np.set_printoptions(precision=2)  # For compact display.
    >>> x = np.array([2, 2, 5, 2, 1, 0, 1, 4, 9])

    Filter with a window length of 5 and a degree 2 polynomial.  Use
    the defaults for all other parameters.

    >>> savgol_filter(x, 5, 2)
    array([1.66, 3.17, 3.54, 2.86, 0.66, 0.17, 1.  , 4.  , 9.  ])

    Note that the last five values in x are samples of a parabola, so
    when mode='interp' (the default) is used with polyorder=2, the last
    three values are unchanged. Compare that to, for example,
    `mode='nearest'`:

    >>> savgol_filter(x, 5, 2, mode='nearest')
    array([1.74, 3.03, 3.54, 2.86, 0.66, 0.17, 1.  , 4.6 , 7.97])