Re: recursion and fsolve

[David Bateman]

According to John W. Eaton <address@hidden> (on 08/04/04):
> On  4-Aug-2004, David Bateman <address@hidden> wrote:
> 
> | F90 allows recursion. Perhaps we should try to use g95 as the basic
> | fortran compiler. We could then add a test to configure.in for 
> | whether the fortran compiler accepts recursion and and enable somthing
> | like the code I suggested...
> 
> You would also have to look at the Minpack code that is the core of
> fsolve (hybrd1 and hybrj1) and determine whether it is actually
> written in a way that would allow a recursive call to work.
>
> There are other cases as well, such as daspk, lsode, etc., which I
> suspect are NOT written with recursion in mind.

What will cause recursion to have problems is if common blocks or save
statements are used. Even that isn't a guarentee that the code won't work
as if the variables in the common or save statements are in fact constants
that are initialized either directly or by a data statement then there 
should be no problem, There are only a couple of potential problems

daspk -> save statement possible problems with ddaspk.f: "SAVE LID, LENID, 
        NONNEG", though not clear why these need saving. With a quick look
        it seems they are re-iniitalize on the next entry. Other SAVE 
        statements in daspk are initialize as constants with a DATA statement

odepack -> contains common block that are definitely used to pass data between
        subroutines. This will cause problems with recursion. However a 
        handy function SRCOM is defined that allows the contents of the 
        common block to be saved and restored. So recursion would be possible
        if this call is used prior to a new call to the solver.

odessa -> similar arguments apply as to odepack

So it seems to me that the recursion issues aren't insurmountable.

D.

-- 
David Bateman                                address@hidden
Motorola CRM                                 +33 1 69 35 48 04 (Ph) 
Parc Les Algorithmes, Commune de St Aubin    +33 1 69 35 77 01 (Fax) 
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