scipy.optimize.root(fun, x0, args=(), method='hybr', jac=None, tol=None, callback=None, options=None)[source]

Find a root of a vector function.

New in version 0.11.0.

Parameters :

fun : callable

A vector function to find a root of.

x0 : ndarray

Initial guess.

args : tuple, optional

Extra arguments passed to the objective function and its Jacobian.

method : str, optional

Type of solver. Should be one of

  • ‘hybr’
  • ‘lm’
  • ‘broyden1’
  • ‘broyden2’
  • ‘anderson’
  • ‘linearmixing’
  • ‘diagbroyden’
  • ‘excitingmixing’
  • ‘krylov’

jac : bool or callable, optional

If jac is a Boolean and is True, fun is assumed to return the value of Jacobian along with the objective function. If False, the Jacobian will be estimated numerically. jac can also be a callable returning the Jacobian of fun. In this case, it must accept the same arguments as fun.

tol : float, optional

Tolerance for termination. For detailed control, use solver-specific options.

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. For all methods but ‘hybr’ and ‘lm’.

options : dict, optional

A dictionary of solver options. E.g. xtol or maxiter, see show_options('root', method) for details.

Returns :

sol : Result

The solution represented as a Result object. Important attributes are: x the solution array, success a Boolean flag indicating if the algorithm exited successfully and message which describes the cause of the termination. See Result for a description of other attributes.


This section describes the available solvers that can be selected by the ‘method’ parameter. The default method is hybr.

Method hybr uses a modification of the Powell hybrid method as implemented in MINPACK [R88].

Method lm solves the system of nonlinear equations in a least squares sense using a modification of the Levenberg-Marquardt algorithm as implemented in MINPACK [R88].

Methods broyden1, broyden2, anderson, linearmixing, diagbroyden, excitingmixing, krylov are inexact Newton methods, with backtracking or full line searches [R89]. Each method corresponds to a particular Jacobian approximations. See nonlin for details.

  • Method broyden1 uses Broyden’s first Jacobian approximation, it is known as Broyden’s good method.
  • Method broyden2 uses Broyden’s second Jacobian approximation, it is known as Broyden’s bad method.
  • Method anderson uses (extended) Anderson mixing.
  • Method Krylov uses Krylov approximation for inverse Jacobian. It is suitable for large-scale problem.
  • Method diagbroyden uses diagonal Broyden Jacobian approximation.
  • Method linearmixing uses a scalar Jacobian approximation.
  • Method excitingmixing uses a tuned diagonal Jacobian approximation.


The algorithms implemented for methods diagbroyden, linearmixing and excitingmixing may be useful for specific problems, but whether they will work may depend strongly on the problem.


[R88](1, 2, 3) More, Jorge J., Burton S. Garbow, and Kenneth E. Hillstrom. 1980. User Guide for MINPACK-1.
[R89](1, 2) C. T. Kelley. 1995. Iterative Methods for Linear and Nonlinear Equations. Society for Industrial and Applied Mathematics. <>


The following functions define a system of nonlinear equations and its jacobian.

>>> def fun(x):
...     return [x[0]  + 0.5 * (x[0] - x[1])**3 - 1.0,
...             0.5 * (x[1] - x[0])**3 + x[1]]
>>> def jac(x):
...     return np.array([[1 + 1.5 * (x[0] - x[1])**2,
...                       -1.5 * (x[0] - x[1])**2],
...                      [-1.5 * (x[1] - x[0])**2,
...                       1 + 1.5 * (x[1] - x[0])**2]])

A solution can be obtained as follows.

>>> from scipy import optimize
>>> sol = optimize.root(fun, [0, 0], jac=jac, method='hybr')
>>> sol.x
array([ 0.8411639,  0.1588361])

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