[petsc-dev] http://www.c-faq.com/aryptr/non0based.html

William Gropp wgropp at illinois.edu
Tue Mar 30 12:55:16 CDT 2010

As long as you have a flat address space, this trick works.  The  
problem is (was) for systems with memory segments; in that case,  
&realarray[-1] might not be valid.


On Mar 30, 2010, at 12:30 PM, Barry Smith wrote:

>    What do the PETSc developers think of this? Is it "otherwise, the  
> behavior is undefined, even if the pointer is not dereferenced."?
>    Whenever we work with global indices like  in FormFunctionLocal()  
> we do this.
>     Is PETSc wrong to ever do this? Is there any other way to allow  
> users to work with global indices in a simple way? Do we need to  
> strip out all the FormFunctionLocals() from PETSc? Not the end of  
> the world but it provides such a nice simple interface for simple  
> problems it seems a pity to toss it.
>    Thanks
>    Barry

William Gropp
Deputy Director for Research
Institute for Advanced Computing Applications and Technologies
Paul and Cynthia Saylor Professor of Computer Science
University of Illinois Urbana-Champaign

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