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I am using Eigen library to which I have to write these vector values from PETSc Vec. tdof is the length of the vector that I need and ei is the number of value in as an index:</div>
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PetscInt ei[tdof];<br class="ContentPasted0">
PetscScalar eveci[tdof];<br>
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for (int i = 0; i < tdof; i++)<br class="ContentPasted1">
ei[i] = i;<br>
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if (nconv>0)
<div class="ContentPasted2"> {</div>
<div class="ContentPasted2"> eval.setZero(nconv);</div>
<div class="ContentPasted2"> evec.setZero(KS.rows(),nconv);</div>
<div class="ContentPasted2"> PetscCall(PetscPrintf(PETSC_COMM_WORLD,</div>
<div class="ContentPasted2"> " k ||Ax-kx||/||kx||\n"</div>
<div class="ContentPasted2"> " ----------------- ------------------\n"));</div>
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<div class="ContentPasted2"> for (int i = 0; i < nconv; i++)</div>
<div class="ContentPasted2"> {</div>
<div class="ContentPasted2"> PetscCall(EPSGetEigenpair(eps,i,&kr,&ki,xr,xi));</div>
<div class="ContentPasted2"> PetscCall(EPSComputeError(eps,i,EPS_ERROR_RELATIVE,&error1));</div>
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<div class="ContentPasted2"> #if defined(PETSC_USE_COMPLEX)</div>
<div class="ContentPasted2"> re = PetscRealPart(kr);</div>
<div class="ContentPasted2"> im = PetscImaginaryPart(kr);</div>
<div class="ContentPasted2"> #else</div>
<div class="ContentPasted2"> re = kr;</div>
<div class="ContentPasted2"> im = ki;</div>
<div class="ContentPasted2"> #endif</div>
<div class="ContentPasted2"> if (im!=0.0) PetscCall(PetscPrintf(PETSC_COMM_WORLD," %9f%+9fi %12g\n",(double)re,(double)im,(double)error1));</div>
<div class="ContentPasted2"> else PetscCall(PetscPrintf(PETSC_COMM_WORLD," %12f %12g\n",(double)re,(double)error1));</div>
<div class="ContentPasted2"> eval(i) = re;</div>
<div class="ContentPasted2"> VecGetValues(xr, tdof, ei, eveci);</div>
<div class="ContentPasted2"> for (int j = 0; j < tdof; j++)</div>
<div class="ContentPasted2"> {</div>
<div class="ContentPasted2"> evec(j, i) = eveci[j];</div>
<div class="ContentPasted2"> }</div>
<div class="ContentPasted2"> }</div>
<div class="ContentPasted2"> PetscCall(PetscPrintf(PETSC_COMM_WORLD,"\n"));</div>
}<br>
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Thank you </div>
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Ali</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Matthew Knepley <knepley@gmail.com><br>
<b>Sent:</b> Tuesday, November 15, 2022 9:43 AM<br>
<b>To:</b> Mohammad Ali Yaqteen <mhyaqteen@sju.ac.kr><br>
<b>Cc:</b> petsc-users@mcs.anl.gov <petsc-users@mcs.anl.gov><br>
<b>Subject:</b> Re: [petsc-users] Reading Vectors from a PETSc Vec</font>
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<div dir="ltr">On Mon, Nov 14, 2022 at 7:39 PM Mohammad Ali Yaqteen <<a href="mailto:mhyaqteen@sju.ac.kr" data-auth="NotApplicable">mhyaqteen@sju.ac.kr</a>> wrote:<br>
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I am using the following procedure to read from Vec, but it keeps giving me the same values! I was told that using VecGetValues gives wrog output.
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<div>By who? It does not give the wrong output.</div>
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<div>You do not show where in the code you define tdof and ei[].</div>
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If not this, then what function should be used to read the contents of a vector?</div>
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<div>I think it would be simpler for you to use VecGetArrayRead(), unless you want values from other processes.</div>
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<div> Thanks,</div>
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<div> Matt</div>
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for (int i = 0; i < nconv; i++)
<div> {</div>
<div> PetscCall(EPSGetEigenpair(eps,i,&kr,&ki,xr,xi));</div>
<div> PetscCall(EPSComputeError(eps,i,EPS_ERROR_RELATIVE,&error1));</div>
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<div> #if defined(PETSC_USE_COMPLEX)</div>
<div> re = PetscRealPart(kr);</div>
<div> im = PetscImaginaryPart(kr);</div>
<div> #else</div>
<div> re = kr;</div>
<div> im = ki;</div>
<div> #endif</div>
<div> if (im!=0.0) PetscCall(PetscPrintf(PETSC_COMM_WORLD," %9f%+9fi %12g\n",(double)re,(double)im,(double)error1));</div>
<div> else PetscCall(PetscPrintf(PETSC_COMM_WORLD," %12f %12g\n",(double)re,(double)error1));</div>
<div> eval(i) = re;</div>
<div> VecGetValues(xr, tdof, ei, eveci);</div>
<div> for (int j = 0; j < tdof; j++)</div>
<div> {</div>
<div> evec(j, i) = eveci[j];</div>
<div> }</div>
<div> }</div>
PetscCall(PetscPrintf(PETSC_COMM_WORLD,"\n"));<br>
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Thank you</div>
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Ali</div>
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<div>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</div>
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<div><a href="http://www.cse.buffalo.edu/~knepley/" data-auth="NotApplicable">https://www.cse.buffalo.edu/~knepley/</a><br>
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