[Shootout-list] Implicitode test

[Simon Geard]

Brent Fulgham wrote:

>--- Sebastien Loisel <sloisel@gmail.com> wrote:
>  
>
>>Hello Simon,
>>
>>Thanks a lot for this implementation, I was dreading
>>writing it. I feel guilty for your hardship, I knew 
>>this test was difficult to implement in Fortran and 
>>many other languages. You have also implemented it 
>>better than I would have. Your criticisms are 
>>accurate, this is not how I use AD in my real code.
>>    
>>
>
>Is this a 'same way' test?  Why can't a Fortran
>programmer solve the problem using the normal Fortran
>idioms and language features?
>
>I think we may just have a lack of communication on 
>this test that has caused Simon to waste a lot of his
>time.
>  
>
Please don't think I'm complaining about the time I spent. I tried the 
implementation because I like f90 and I like Numerical Analysis and 
thought that this test should be a good vehicle for f90.

The point I'm trying to make is that this program is more than 'Hello 
World' and most implementers are going to spend some time debugging 
their code. The use of AD makes this much harder (because of the 
indirection) whilst not providing (at least in the Newton case) any 
numerical benefit. I'd suggest on the basis of my experience that 
implementers use a finite difference approximation to the first 
derivative in the first instance and when the numbers are about right 
add in the AD code.

Simon