On Fri, Apr 15, 2011 at 4:28 AM, khalid ashraf <span dir="ltr"><<a href="mailto:khalid_eee@yahoo.com">khalid_eee@yahoo.com</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div><div style="font-family:arial, helvetica, sans-serif;font-size:12pt"><div>Hi,</div><div>I am running src/ksp/ksp/examples/tutorials/ex22.c</div><div>I matched the output of single processor and multiprocessor results and it works fine.</div>
<div>But I want to use a periodic boundary condition. I make the following changes in the main function and this works fine with this change as well:</div><div><br></div><div><div> ierr = DMMGCreate(PETSC_COMM_WORLD,1,PETSC_NULL,&dmmg);CHKERRQ(ierr);</div>
<div> ierr = DACreate3d(PETSC_COMM_WORLD,DA_XYZPERIODIC,DA_STENCIL_STAR,10,10,2,PETSC_DECIDE,PETSC_DECIDE,PETSC_DECIDE,1,1,0,0,0,&da);CHKERRQ(ierr);</div><div><br></div><div><br></div><div>However, when I comment out these following lines since I am using a PBC, then the result of 1 proc and multi-proc are not the same. They vary within 5 decimal points and
the difference increases with increasing number of processors. </div></div></div></div></blockquote><div><br></div><div>The periodic operator has a null space. You must put that in the solver DMMGSetNullSpace(), so that it is projected out at each step.</div>
<div><br></div><div> Matt</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div><div style="font-family:arial, helvetica, sans-serif;font-size:12pt">
<div><div>/* if (i==0 || j==0 || k==0 || i==mx-1 || j==my-1 || k==mz-1){</div><div><div> v[0] = 2.0*(HxHydHz + HxHzdHy + HyHzdHx);</div><div> ierr = MatSetValuesStencil(B,1,&row,1,&row,v,INSERT_VALUES);CHKERRQ(ierr);</div>
<div> } else */</div><div><br></div><div>Could you please tell me what is going wrong here.</div><div><br></div><div>Thanks.</div></div></div><div></div>
</div></div></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>