Exponent from corey's model for relative permeability

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What steps will reproduce the problem?
1. Define either the nw or no parameter in the input file as a non-natural 
number
2.
3.

What is the expected output? What do you see instead?
The program should handle without problems any real number for these 
parameters. Insted it is generating a singular matrix if any non-natural number 
is given as input.

Please use labels and text to provide additional information.
The following error message is showed:
UMFPACK problem related to call to numeric *** Warning: UMFPACK reports that 
the matrix being solved is singular. UMFPACK problem related to call to solve

In the following links seem that someone has already had similar issues with 
Dolfin/UMFPACK:
https://answers.launchpad.net/dolfin/+question/168115
https://answers.launchpad.net/dolfin/+question/149194

Original issue reported on code.google.com by bruno...@yahoo.com.br on 21 Nov 2011 at 1:45

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Possible reason for the problem:
Maybe due to the floating point operations truncation error or due to the 
oscillations in the solution, the non-natural exponent is being applied to a 
negative base (Sw^nw, with Sw<0.0 and nw non-natural), what leads to an answer 
in the complex domain (Ex: -2^(0.5) = sqrt(2)*i).

Original comment by bruno...@yahoo.com.br on 21 Nov 2011 at 4:39

• Changed title: Exponent from corey's model for relative permeability

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Original comment by bruno...@yahoo.com.br on 21 Nov 2011 at 4:39

• Added labels: Priority-High
• Removed labels: Priority-Medium