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<DIV><FONT color=#0000ff size=2 face=Verdana>petsc teams,</FONT></DIV>
<DIV><FONT color=#0000ff></FONT> </DIV>
<DIV><FONT color=#0000ff>When I use SNES, I find my program iterated many
times but x vector and residual vector</FONT></DIV>
<DIV><FONT color=#0000ff></FONT> </DIV>
<DIV><FONT color=#0000ff>remained unchanged, that is to say,no convergence.I
used finite difference jacobian approximations,</FONT></DIV>
<DIV><FONT color=#0000ff></FONT> </DIV>
<DIV><FONT color=#0000ff>but I cannot confirm the jacobian matrix structure is
right.Whether the matrix structure will influence</FONT></DIV>
<DIV><FONT color=#0000ff></FONT> </DIV>
<DIV><FONT color=#0000ff>the convergence of SNES or not? Why does my x
vector and residual vector <FONT color=#0000ff>remained
unchanged?</FONT></FONT></DIV>
<DIV><FONT color=#0000ff></FONT> </DIV>
<DIV>
<DIV>
call FormJacobian(snes,x,J,J,flag,dummy,ierr)</DIV>
<DIV> call MatGetColoring(J,MATCOLORING_SL,iscoloring,ierr)</DIV>
<DIV> call MatFDColoringCreate(J,iscoloring,fdcoloring,ierr)</DIV>
<DIV> call ISColoringDestroy(iscoloring,ierr)</DIV>
<DIV> call MatFDColoringSetFromOptions(fdcoloring,ierr)</DIV>
<DIV> call MatFDColoringSetFunction(fdcoloring,FormFunction,</DIV>
<DIV> & PETSC_NULL_OBJECT,ierr)</DIV>
<DIV> call SNESSetJacobian(snes,J,J,SNESDefaultComputeJacobianColor,</DIV>
<DIV> & fdcoloring,ierr)</DIV>
<DIV> call SNESGetKSP(snes,ksp,ierr)</DIV>
<DIV> call KSPGetPC(ksp,pc,ierr)</DIV>
<DIV> call SNESSolve(snes,PETSC_NULL_OBJECT,petscu,ierr)</DIV>
<DIV><FONT color=#0000ff>Thanks,</FONT></DIV>
<DIV><FONT color=#0000ff>leping</FONT></DIV></DIV>
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