[GRASS-dev] Re: v.surf.rst

[Soeren Gebbert]

Helo,

2010/5/3 Abhishek Shukla <abhishekiiith at gmail.com>:
>
>
> On Mon, May 3, 2010 at 1:45 AM, Soeren Gebbert
> <soerengebbert at googlemail.com> wrote:
>>
>> Hello,
>> LU is used to solve the linear equation system, because the matrix is
>> not positive definite. There is a zero at the diagonal. You can try to
>> sort the rows and cols, but i'm not sure if the matrix will get
>> positive definite. Maybe an LDL decomposition can be used instead of
>> LU.
>> I have tried to solve the linear equation system with a parallele
>> BiCGStab algorithm, but most of the time the linear equation system is
>> of very bad condition, so the BiCGStab solver fails. An LU algorithm
>> with pivoting is needed.
>>
>> Hence, reordering rows and cols to avoid a zero at the diagonal and
>> parallel LDL decomposition may be the best choice.
>>
>
>
> I believe  you meant LDU decomposition here.

Nope, i mean LDL. Ok, the mathematical correct description is LDL^T.

http://www.cise.ufl.edu/research/sparse/ldl/

Best regards
Soeren