<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On May 5, 2010, at 10:08 AM, Matthew Knepley wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">Try using -snes_mf which will approximate the Jacobian automatically.</blockquote><div><br></div> You can also use -snes_type test -snes_test_display (for a small problem). Also try runs with -snes_monitor -ksp_monitor -ksp_converged_reason -snes_converged_reason and try also -info for lots of information about the line search. </div><div><br></div><div> You can also try running with -pc_type lu to eliminate any chance that failure of the linear solver is the problem.</div><div><br></div><div><br></div><div> Barry</div><div><br><blockquote type="cite"><div><br></div><div> Matt<br><br><div class="gmail_quote">2010/5/5 ³ÂÀÖƽ£¨Leping Chen£© <span dir="ltr"><<a href="mailto:chenleping@yahoo.cn">chenleping@yahoo.cn</a>></span><br>
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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>
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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>
<div><font size="2" face="Verdana"><font color="#c0c0c0" size="2" face="Verdana"><font size="2" face="Verdana"><font color="#c0c0c0" size="2" face="Verdana"><font color="#000000"><font color="#0000ff" size="3" face="ËÎÌå"></font> </font></font></font></font></font></div>
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</blockquote></div><br><br clear="all"><br>-- <br>What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>-- Norbert Wiener<br>
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