Zhisong Qu

Good idea. I would suggest we open an Overleaf Latex document that shared among everyone. The document can then be integrated into `manual.h` permanently.

I added a section talking about SPEC/VMEC sign conversion. Please see if you agree or not before we forget...

> * in-place debugging code --> separable into stand-alone unit tests? This should be the way to go. A neater code will be preferable. We can move the testing codes...

> Hi, > > I am trying to understand what is going on in `mtrxhs.f90`, and how it is used to evaluate the derivatives of the field w.r.t the geometry...

We can also explore other open source scientific libraries such as PETSc, GSL, NLOPT and so on, which contain lots of nonlinear solvers and optimization algorithms. Many of them come...

It seems that Lconstraint only works for the linear solver (LBeltrami=4). For LBeltrami=2, the option Lconstraint is not used.

I have benchmarked the helicity constraint with the Taylor analytic solution in the cylindrical geometry. It seems to match quite well.  The Mathematica file that generates this plot is...

My understand is, dMA, dMB are used for any methods. The different methods are different algorithms to minimize the energy functional in the quadratic form (or cubic for \mu *...

And my worry is that, the matrix dMA - \mu dMB in bifurcation cases (e.g. helical Taylor states) will be singular and non-invertible, since \mu is the eigenvalue. Therefore, we...

I have attached a derivation of how the Hessian should be found. Please see if you agree or not. @jloizu @SRHudson [Hessian.pdf](https://github.com/PrincetonUniversity/SPEC/files/2780909/Hessian.pdf)