Questions tagged [newton-method]
Method for finding successively better approximations to the roots (or zeroes) of a real-valued function
7
votes
1answer
153 views
Imbalance of variables in Mixing Newton's method and Linear solver for a Non-linear system
Problem
Solving a non-linear system of equations.
The number of variables is the same as the number of equations.
When I fix a set of variables (say $\vec{y}$) and keep another set free (say $\vec{...
1
vote
1answer
81 views
Newton's method problem
I struggle with this problem:
I understand how to apply Newton's method to a already given function but I can't seem to find that function in this case from the given input n, t, d and s. I'm ...
1
vote
1answer
68 views
Root finding using Newton's method with quadratic interpolation - Is there a mistake in this textbook?
I've been trying to learn about root finding using Newton's method, which uses a quadratic interpolating polynomial. I found this text, Numerical methods for roots of polynomials, PART 2: McNamee &...
1
vote
1answer
36 views
Muller's method is the same as Newton's method with a quadratic interpolating polynomial?
I'm new to numerical analysis, and have been learning root finding algorithms. I am a bit confused about the difference between Muller's method, and Newton's method using an n-degree interpolating ...
3
votes
0answers
93 views
Difference between Dishonest Newton method and Very Dishonest Newton method
What is the difference between the Dishonest Newton method and the Very Dishonest Newton method? Is there a difference or do they mean the same thing?
I have tried searching for this on the internet ...
2
votes
0answers
63 views
Which SciPy nonlinear solver when Jacobian is analytically known and sparse?
I have a nonlinear function fun with n inputs and n outputs. I also have a function jac which calculates the Jacobian, which is ...
0
votes
0answers
32 views
Obtaining increment for a variable in this paper
I need to estimate a solar panel's model using datasheet data, and I am stating with this paper.
My issue is that I don't know how to get an increment for $n$ in
the Newton-Raphson method requires me ...
1
vote
0answers
102 views
How to prevent BFGS from getting stuck on astronomically large gradient?
I have implemented BFGS myself from scratch in order to solve minimization problems. Part of BFGS, as I understand it, is that the approximation to the Hessian is supposed to be positive definite, ...
1
vote
2answers
648 views
How does one calculate reaction force in FEA?
I wrote a UEL (User Element in Abaqus) for one element and compared to a reference UEL which used standard FEM, where the results agreed satisfactorily, except the reaction force. The stress, strain, ...
5
votes
1answer
114 views
Can redundant variables be beneficial for root-finding convergence
Suppose I have $n$ generally nonlinear equations for $n$ variables, like e.g. for $n=2$ the system $F(x,y)=0$
$$
\begin{aligned}
x^2+2y-4&=0\\
\sqrt{8}x+y^2-5&=0
\end{aligned}
$$
By ...
0
votes
2answers
112 views
Nédélec Elements and Newton-Methods
If you want to develop numerical algorithms for variational inequalities, you often choose a Semismooth Newton Method. In many cases, this approach involves derivatives of $\max$ or $\min$ functions ...
5
votes
2answers
181 views
How to calculate/derive analytic FEM Newton Jacobian
I trying to wrap my head of derivation of the analytic FEM Jacobian
for the Newton method. Say we have a nonlinear Poisson problem of the
(weak) form
$$ \int a(u)\nabla\ u\cdot \nabla v = \int f v $$
...
1
vote
0answers
115 views
Vectorised root finding in Python
I have an array of size (254, 80) which I am trying to use Scipy's fsolve on. I have found that the speed of using fsolve on a vector is quicker than it is in a for loop but only for vectors upto ...
1
vote
0answers
123 views
Newton - Raphson method : maxima of function in 2 variables
I am computing the maximum of a function (with two-variables) using Newton-Raphson method. The function is : $e^{-(x \ - x_0)^2 - (y \ - y_0)^2}$, whose maxima exists at $(x_0,y_0)$.
The Jacobian ...
4
votes
3answers
139 views
How can I use Projected Gradient Descent for this optimization problem with constraint?
Suppose $ q $ and $ A $ are given and that $ q, p \in R^{N} $ and $ A \in R^{NxN} $, then how can I find the vector $ p $ such that
$$ (q - p)^{T}A(q - p) $$ is minimized constraint to $ \sum_{i=1}^{...
1
vote
0answers
70 views
Successive iteration method for solving eigenvalue ploblem
I have a question concerning the branch of successive iteration methods (Newton, Runge-Kutta). I definitely know (or can read in Wikipedia) the implementation of these methods. But I was wondering ...
1
vote
0answers
83 views
Jacobian of the electron and hole drift diffusion equations with respect to potential in semiconductors
These are the discretized drift diffusion equations as taken from the book "Analysis and Simulation of Semiconductor Devices". The electron continuity equation is:
$$((\Delta_{j-1}^y+\Delta_j^y)/2\...
2
votes
1answer
108 views
Newton's method stagnates at small error
I have a system of the form
$$A(u)f(u)=b$$
where $A$ is basically a matrix originating from the Finite Element Method.
I try to solve it using the Newton method:
$$R = A(u_{i}) f(u_{i}) - b $$
$$...
1
vote
0answers
77 views
Using Newton-Raphson method to solve the hydrostatic equation
I'm trying to use newton-raphson method for nonlinear systems of equations as described in 'Numerical recipies' book in chapter 9.6 to solve the hydrostatic equation for a polytropic star.
For each ...
6
votes
1answer
491 views
Newton's method with box-constraints
I have to use an iterative method (Newton-Raphson, modified Newton and Broyden) to solve a system of nonlinear equations $f(x)=0$. Every unknown $x_i$ is bounded between $l_i$ and $u_i$, i.e., $l_i<...
3
votes
0answers
92 views
Optimization based integration for MPM
I'm considering implementing (just for simplicity) the unconstrained implicit optimization based integration for Material Point Method as described in Chenfanfu Jiang's thesis on MPM (the minimization ...
2
votes
0answers
120 views
Does applying the Newton-Raphson iteration for matrix reciprocal refine a matrix inverse from LU/GE?
This is a follow-up to this answer.
Suppose you have a possibly very ill-conditioned matrix $A$, and you compute its inverse with LU/GE to get $X_{\text{lu}}\approx A^{-1}$.
The Newton-Raphson ...
7
votes
1answer
172 views
What would be a good approach to solving this large data non-linear least squares optimisation
Introduction to Problem
I'm using a Truncated Signed Distance Function to perform 3D reconstruction from depth images.
Essentially I have a large voxel grid where each voxel contains the signed ...
2
votes
2answers
339 views
Low-rank updates in BFGS
I have read this and other threads on this site on BFGS, but I still don't have a clear understanding of what it's meant by low-rank updates.
For example, I read the following in this book:
The ...
2
votes
1answer
57 views
Doubt regarding principled approach towards approximating the Hessian
In my optimization problem, the hessian has a structure such that it can be written as the sum of two matrices. Populating the first of the matrices is efficient. Populating the second one is ...
7
votes
1answer
268 views
Eigenvalues of $ab^T$
In deriving a Newton scheme, I end up with a Jacobian matrix of the form $J=I+ab^T$ where $a,b$ are vectors. For practical reasons, I want to approximate it by a symmetric positive definite matrix. ...
6
votes
1answer
119 views
Roots of a function for eigensystem
I want to find the roots for $\kappa$ for the equation
$$\sqrt{\alpha - 1} \cos{\left (\frac{\sqrt{2} \sqrt{\alpha - 1}}{2 \sqrt{\epsilon}} \right )} \cosh{\left (\frac{\sqrt{2} \sqrt{\alpha + 1}}{2 \...
1
vote
0answers
88 views
Quasi Newton taking very small steps
I have implemented a Quasi-Newton method based on the Hessian approximation. I am noticing that the algorithm takes too many iterations to converge, even though it does converge. What I am not able to ...
1
vote
1answer
89 views
The linear system in Quasi Newton method
I have implemented a Quasi Newton method for my problem, where I use the Hessian matrix approximation based approach. Hence, there is a linear system solve in every iteration. I solve the linear ...
1
vote
0answers
105 views
Solving a large system of nonlinear equations, where timeseries are the unknown
I am trying to solve a problem, which I find quite hard, like, headache-hard. I have to solve the following set of $M$ nonlinear equations:
$$F(X)=\begin{bmatrix}f_1 (X)\\f_2 (X)\\...\\f_M (X)\\ \end{...
0
votes
0answers
116 views
What does a negative time stepping mean? (Adaptive time stepping)
Summary behind the problem: The following code aims at solving a static elasto-plastic problem. Like a 2D square mesh based on an elasto-plastic constitutive model like Von-Mises or Drucker-Prager ...
8
votes
1answer
99 views
Are there special methods for solving $f'(z)=0$ for analytic $f$?
I am trying to solve a bunch of equations for the zeros of the derivative of an analytic function, and I would like to know if there exist methods that exploit this structure to provide better ...
10
votes
3answers
564 views
Methods of solving non-linear advection-diffusion systems beyond Newton-Raphson?
I'm working on a project where I have two adv-diff coupled domains through their respective source terms (one domain adds mass, the other subtracts mass). For brevity, I'm modeling them in steady ...
3
votes
0answers
216 views
Quasi Newton method for block diagonal Hessian
I am having an unconstrained optimization problem, where the Hessian is positive semidefinite and block diagonal. The function is strictly convex, hence, the curvature condition ($ s^{T}_{k}y_{k} > ...
2
votes
0answers
191 views
Applying Newton-Raphson method to system of two differential equations, one time independent, one time dependent
The goal is to couple system of two nonlinear differential equations by applying appropriate space and time discretization and Newton-Raphson scheme.
The equations system is
$$\left[
\begin{array}{c}
...
2
votes
2answers
179 views
Why do Newton-Krylov iterations stagnate in this problem? [closed]
Consider this integro-differential heat equation taken from SciPy documentation page:
$
\nabla^2 P = \alpha \left(\iint_\Omega \cosh(P)dx dy \right)^2
$
which was found in this question.
In the ...
4
votes
1answer
156 views
Efficient and stable computation of inverse CDF
What is the most efficient and numerically stable algorithm for computing the inverse CDF $F^{-1}(y)$ of a probability function, assuming that both the PDF $f(x)$ and the CDF $F(x)$ are known ...
5
votes
1answer
229 views
Solving a set of linear equations with block structure and weak coupling
I have a standard set of linear equations $Ax=b$ where the Hessian matrix $A$ has the special block structure as shown:
$A=
\begin{pmatrix}
T & U\\
U^T & V
\end{pmatrix}$,
$x=
\begin{...
3
votes
1answer
378 views
Implementation of Backward-Euler scheme, Newton-Raphson iteration scheme to time dependent nonlinear differential equation
I just knew how to do Newton-Raphson iteration in time-independent 1D nonlinear differential equation. Then I applied to time-dependent 1D nonlinear differential equation, and I got confused.
Below ...
4
votes
0answers
255 views
Best way to add a positivity constraint to Newton's Method
So given an objective function $f({\bf x})$, I would like to include a positivity constraint when I perform the fixed point iteration:
$${\bf x}^{(t+1)}={\bf x}^{(t)} - \text{H}_f^{-1}\nabla f({\bf x}^...
1
vote
2answers
554 views
How to implement Newton method in solving 1D PDE system? (ie. Poisson eq, continuity eq, drift-diffusion eq.)
I want to solve PDE system, which consists of Poisson equation, continuity equations for electron and hole with drift-diffusion equation numerically, by using method called Newton's method.
This ...
4
votes
1answer
844 views
Newton's method goes to zero determinant Jacobian
I am using the Newton's method to solve $3\times3$ systems.
For some particular cases, it turns out that at a given iteration, the Jacobian matrix cannot be inverted and that its determinant is very ...
5
votes
1answer
2k views
Difference between Gauss-Newton method and quasi-Newton method for optimization
Can anybody help me? I heard that Gauss-Newton method compute an aproximation of the Hessian instead of the true Hessian, but, quasi-Newton method too, don't it? what is the differences between them?
...
1
vote
1answer
129 views
Solving this nonlinear system of equations
Suppose I have this set of equations:
$$a = x + z\qquad (1)$$
$$b = y + \frac{z}{2}\qquad (2)$$
$$ z = k_0x\sqrt{y}\qquad (3)$$
Where $a$, $b$ $\in \mathbb{R}$ and $k_0 > 0$. The values of $a$ ...
8
votes
1answer
448 views
Newton iteration applied to nonlinear PDE
I'm having difficulty understanding how to apply Newton iteration to nonlinear PDEs and then use a fully implicit scheme to time step. For example, I want to solve Burgers equation
$$u_{t} + u u_{x} -...
1
vote
1answer
255 views
Inverse Transformation of Isoparametric Quadrilaterals
I urgently need help with a problem I am having for an assignment for university. I do not expect a full solution, but I am really in need of guidance.
I am required to write a FEA program in VBA, I ...
2
votes
2answers
223 views
Ill-conditioned Jacobian matrix from Nernst-Planck equation with Butler-Volmer reactions
The governing equations are listed here of my notes on page 4. It's a reproduction of other's paper which solves the equations with COMSOL. The problems arise when I want to solve for the consistent ...
1
vote
0answers
75 views
Monotonic convergence of Newton's method for boundary value problems [closed]
I’m interested in solving nonlinear elliptic boundary value problems of the type
$$
-a\Delta u + f(u) = 0,
$$
$$
u|_\Gamma = u_0
$$
by Newton’s method when its convergence is global and monotonic.
...
1
vote
0answers
240 views
Linearization of two phase flow iteration for Newton Method
I am trying to implement a numerical model to solve a two-phase flow using the Newton-Raphson method. To do so, I also have to differentiate the fluid pressure $P$ with respect to the matrix velocity $...
5
votes
1answer
349 views
scaling and preconditioning for trust region Newton methods
Geometrically, scaling and preconditioning seem to address similar challenges in optimization. However, these two concepts are implemented very differently. Take trust region Newton method, as an ...
