Module « scipy.optimize »

Fonction anderson - module scipy.optimize

Signature de la fonction anderson

def anderson(F, xin, iter=None, alpha=None, w0=0.01, M=5, verbose=False, maxiter=None, f_tol=None, f_rtol=None, x_tol=None, x_rtol=None, tol_norm=None, line_search='armijo', callback=None, **kw) 

Description

anderson.__doc__

    Find a root of a function, using (extended) Anderson mixing.

    The Jacobian is formed by for a 'best' solution in the space
    spanned by last `M` vectors. As a result, only a MxM matrix
    inversions and MxN multiplications are required. [Ey]_

    Parameters
    ----------
    F : function(x) -> f
        Function whose root to find; should take and return an array-like
        object.
    xin : array_like
        Initial guess for the solution
    alpha : float, optional
        Initial guess for the Jacobian is (-1/alpha).
    M : float, optional
        Number of previous vectors to retain. Defaults to 5.
    w0 : float, optional
        Regularization parameter for numerical stability.
        Compared to unity, good values of the order of 0.01.
    iter : int, optional
        Number of iterations to make. If omitted (default), make as many
        as required to meet tolerances.
    verbose : bool, optional
        Print status to stdout on every iteration.
    maxiter : int, optional
        Maximum number of iterations to make. If more are needed to
        meet convergence, `NoConvergence` is raised.
    f_tol : float, optional
        Absolute tolerance (in max-norm) for the residual.
        If omitted, default is 6e-6.
    f_rtol : float, optional
        Relative tolerance for the residual. If omitted, not used.
    x_tol : float, optional
        Absolute minimum step size, as determined from the Jacobian
        approximation. If the step size is smaller than this, optimization
        is terminated as successful. If omitted, not used.
    x_rtol : float, optional
        Relative minimum step size. If omitted, not used.
    tol_norm : function(vector) -> scalar, optional
        Norm to use in convergence check. Default is the maximum norm.
    line_search : {None, 'armijo' (default), 'wolfe'}, optional
        Which type of a line search to use to determine the step size in the
        direction given by the Jacobian approximation. Defaults to 'armijo'.
    callback : function, optional
        Optional callback function. It is called on every iteration as
        ``callback(x, f)`` where `x` is the current solution and `f`
        the corresponding residual.

    Returns
    -------
    sol : ndarray
        An array (of similar array type as `x0`) containing the final solution.

    Raises
    ------
    NoConvergence
        When a solution was not found.

    See Also
    --------
    root : Interface to root finding algorithms for multivariate
           functions. See ``method=='anderson'`` in particular.

    References
    ----------
    .. [Ey] V. Eyert, J. Comp. Phys., 124, 271 (1996).

    Examples
    --------
    The following functions define a system of nonlinear equations

    >>> def fun(x):
    ...     return [x[0]  + 0.5 * (x[0] - x[1])**3 - 1.0,
    ...             0.5 * (x[1] - x[0])**3 + x[1]]

    A solution can be obtained as follows.

    >>> from scipy import optimize
    >>> sol = optimize.anderson(fun, [0, 0])
    >>> sol
    array([0.84116588, 0.15883789])