DMMG solver convergence with single precision?

[Chris Cooper]

Hi,

Just wondering if there are any techniques for improving DMMG 
convergence on a linear problem when operating in single precision?

eg using ksp example 34 in Petsc 2.3.3 with multigrid levels changed to 6...

double precision:
  0 KSP Residual norm 4.451733404502e-02
  1 KSP Residual norm 2.801676364873e-04
  2 KSP Residual norm 3.215426166316e-06
  3 KSP Residual norm 5.446277176355e-08
Residual norm 5.44628e-08
Error norm 0.000356798
Error norm 9.21724e-05
Error norm 1.34208e-07

single precision:
  0 KSP Residual norm 4.450287297368e-02
  1 KSP Residual norm 2.799208450597e-04
  2 KSP Residual norm 2.232483529951e-05
  3 KSP Residual norm 1.575733222126e-05
  4 KSP Residual norm 1.286925271415e-05
...
 27 KSP Residual norm 4.369261660031e-06
 28 KSP Residual norm 4.287577212381e-06
 29 KSP Residual norm 4.210308816255e-06
 30 KSP Residual norm 2.235170904896e-05
 31 KSP Residual norm 1.709007477757e-07
Residual norm 8.45584e-07
Error norm 0.000370784
Error norm 9.54664e-05
Error norm 1.38935e-07

thanks,
Chris Cooper
Animal Logic

Animal Logic
http://www.animallogic.com

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