<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">Hi Mark!<br><div><br><blockquote type="cite"><div>On Sep 9, 2023, at 06:40, Mark Adams <mfadams@lbl.gov> wrote:</div><br class="Apple-interchange-newline"><div><div dir="ltr"> PetscFECreateLagrange(comm, dim, 1, simplex, 1, PETSC_DETERMINE, &fe);<div><br></div><div>The default may be qorder = 0.</div><div>Replace PETSC_DETERMINE with 1, 2, etc, and see.</div></div></div></blockquote><div><br></div><div>With PETSC_DETERMINE, I see 4 evaluations of the function per element, so I think that works as expected.</div><div>Even if I force a higher quadrature order, I still see the wrong value.</div><div><br></div><div>—</div><div>David</div><br><blockquote type="cite"><div><div dir="ltr"><div><br></div><div>Thanks,</div><div>Mark</div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Sep 8, 2023 at 6:26 PM David Andrs <<a href="mailto:andrsd@gmail.com">andrsd@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi all!<br>
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I am trying to use DMPlexComputeIntegralFEM to compute an integral $\int_\Omega u d\Omega$. My domain is a square (-1, 1)^2 (2x2 QUAD4 elements), I add first order Lagrange FE field on it, set the solution vector (computed by a previous simulation).<br>
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The value I am seeing computed by PETSc is -4, but the hand-calculated value of this integral is -4.6. I also checked this in paraview using the ‘Integrate Variables’ filter and it also returns -4.6 (this was to double check that my hand-calculated value is correct).<br>
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So, I must be missing something obvious in my code. Attached is the minimal PETSc code to show what I am doing. This is against PETSc 3.19.4.<br>
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Thanks in advance for your help,<br>
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David<br>
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