Optimization Method
Numerical algorithms solve non-linear least squares problems by iteratively updating parameter estimates. The levenberg-marquardt algorithm achieves this by interpolating between the gradient descent method and the Gauss-Newton method.
Algorithmic Balance
A damping factor adjusts the behavior of the optimization step based on the local curvature of the error surface. When the current estimate is far from the minimum, the levenberg-marquardt routine increases this factor to behave like gradient descent. As the estimate approaches the solution, the damping factor decreases to enable rapid quadratic convergence.
This adaptive stepping protects the calculation from diverging in poorly behaved regions.
Convergence Behavior
Iterative matrices are constructed using the jacobian of the system of non-linear equations. Calculations with the levenberg-marquardt approach use this matrix to update the parameter vectors. If the updated vector reduces the sum of squared errors, the step is accepted and the damping factor is reduced.
Otherwise, the damping factor increases and the step is recalculated with a smaller, safer step size.
Application Boundary
Large-scale optimization problems with thousands of variables can exceed the memory capacity required for dense matrix inversion. This limitation occurs because the levenberg-marquardt process must solve a linear system at every iteration. Sparse matrix solvers or alternative conjugate gradient techniques are employed when the Jacobian matrix becomes too large.
Highly non-convex surfaces may still trap the algorithm in local minima instead of finding the global optimum.