[petsc-users] matrix with complex number

Barry Smith bsmith at mcs.anl.gov
Fri Jan 22 22:29:40 CST 2010


    Thanks for the suggestion. I've played around with this approach  
over the years, but given the size of PETSc I've always been too  
frightened by the uglyness and complexity of maintaining such code. It  
also doesn't cleanly handle mixing objects of different types  
together. For example, from a user perspective it is completely  
reasonable to try to multiply a complex vector by a real matrix, or  
conversely a real vector by a complex matrix, or to put real values  
into a complex matrix or vector but providing support for this  
requires even more "templating-like" stuff with macros.


On Jan 22, 2010, at 10:23 PM, Hal Finkel wrote:

> Barry,
> I've used the following process to achieve a similar effect in C  
> projects:
> Modify the make files to build each source file multiple times, once  
> for each base type (float, double, double complex, etc.). The type  
> is selected via a preprocessor definition provided on the command  
> line (-DUSE_FLOAT, -DUSE_DOUBLE, etc.). A prefix or suffix specific  
> to each type is appended to the name of the resulting object file  
> (so that they're unique). Also, the function names (and all other  
> global symbols) in each file are wrapped with a function-like macro  
> which appends a prefix or suffix depending on the current type  
> selected. In this way, everything can be included in one library  
> without conflict or unnecessary code duplication.
> -Hal
> Barry Smith wrote:
>>   The issue is that PETSc is written in C and there are not C++  
>> templates in C. We do not want to write TWO copies of each file,  
>> one with dcomplex everywhere and another with double everywhere and  
>> give different names to the functions in each language. It would be  
>> a pain to write and maintain and a pain to use. Who wants to write  
>> MatSolve() to solve with real numbers and MatSolveComplex() to  
>> solve with complex?
>>  C++ templates can be used to make all this possible but they are  
>> not perfect to the task. Basically we need a better language to  
>> allow easy mixing of dcomplex and double.
>>   Barry
>> On Jan 22, 2010, at 2:43 PM, Yujie wrote:
>>> Dear Barry,
>>> What are the difficult things if PETSc is revised with matrices of  
>>> complex and real numbers? It should be more flexible for a general  
>>> scientific toolbox. I am curious almost all the packages don't  
>>> support both simultaneously. Thanks a lot.
>>> Regards,
>>> Yujie
>>> On Fri, Jan 22, 2010 at 2:35 PM, Barry Smith <bsmith at mcs.anl.gov>  
>>> wrote:
>>>  The way we handle complex numbered linear systems in PETSc is to  
>>> compile all of PETSc with complex numbers and then just use the  
>>> solvers on those complex numbers. The current drawback to this is  
>>> that PETSc can only be built with support for complex numbers or  
>>> for real numbers. We cannot build a PETSc where some matrices are  
>>> complex and some are real.
>>> We don't have any interest in solving complex systems as larger  
>>> real systems.
>>>  Barry
>>> On Jan 22, 2010, at 11:04 AM, Yujie wrote:
>>> Dear PETSc Developers,
>>> Recently, I am trying to find some complex number-based solvers  
>>> and preconditioners. However, it is difficult to find a general  
>>> framework to include some solvers and preconditioners. Trilinos is  
>>> developing a package, komplex, to use the real-number-based solver  
>>> to solve complex number -based problem. I don't know whether PETSc  
>>> wants to develop such the function for complex number-based  
>>> problem. I think it will significantly increase the application  
>>> range of PETSc. After all, in PETSc, lots of solvers and  
>>> preconditioners have been developed. Thanks  a lot.
>>> Regards,
>>> Yujie

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