Re: [eigen] solve with and without check

[Benoit Jacob <jacob.benoit.1@xxxxxxxxx>]

2009/8/24 Andrea Arteaga <yo.eres@xxxxxxxxx>:
>> --> i propose the following change:
>> in all decompositions that have a solve() checking for existence,
>> let's rename solve() to solveWithCheck()   (or whatever native English
>> speakers prefer... perhaps trySolve() ? checkSolve() ? )
>> then let's add a method solve() that doesn't do any check, making it
>> the responsibility of the caller that a decent solution exists.
>
> Or the opposite.
> For example if one want to access to a matrix without control, has to use the coeff() or coeffRef()
> methods, while the operator() (i.e. the primary choice) makes a control. In order to ensure the
> consistency with the other parts of Eigen, the solve() method should make a control, while another
> method (solveWithoutCheck() or whatever) should return the solution without performing the check.

Here we have a bad case of conflicting principles:

"The safest should be the default"

versus

"The most common should be the default"

For operator() versus coeff(), it was an easy choice because in most
cases the user wants the check, and can always disable it by disabling
asserts.

Here it's different, solveWithCheck is probably not the most common case.

Let me stress the problem a bit more: the current solve isn't too
reliable to determine when a solution exists. The cause of this
problem is that our triangular solvers don't do that check. The reason
why they don't is presumably that it would be costly for them to, but
perhaps that's worth checking. Gael, could triangular solvers be
extended to support 0's on the diagonal and detect inexistence of
solutions ?

Benoit