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<div style="font-size: 12pt; color: rgb(0, 0, 0);"><font face="-webkit-system-font, Helvetica Neue, Helvetica, sans-serif">petsc's QN routines uses limited-memory variable metric format, which means explicit hessian is not constructed.</font></div>
<div style="font-size: 12pt; color: rgb(0, 0, 0);"><font face="-webkit-system-font, Helvetica Neue, Helvetica, sans-serif">Instead of creating explicit hessian, TAO uses MatSolve, and MatMult, to "access" the hessian. So you can have access to Hx, and H^{-1}x,
but not H matrix by itself. </font></div>
<div style="font-size: 12pt; color: rgb(0, 0, 0);">And as of right now, there isn't a way to access such Hx, and H^{-1}x. (which also means that even if the routines to access Hx, H^{-1}x were there, getting those at each iteration doesn't really show much
information, I think.)</div>
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<div style="font-size: 12pt; color: rgb(0, 0, 0);"><font face="-webkit-system-font, Helvetica Neue, Helvetica, sans-serif"><span style="font-size: 12pt;">(Sorry for email reply-chain screw up..)</span></font></div>
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<div><span style="margin:0px"><span style="font-family: -webkit-system-font, "Helvetica Neue", Helvetica, sans-serif; margin: 0px; color: black;"><b>From:<span> </span></b></span><span style="margin:0px">Stefano Carli <stefano.carli@kuleuven.be><br>
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<div style="margin:0px"><span style="font-family: -webkit-system-font, "Helvetica Neue", Helvetica, sans-serif; color: black;"><b>Subject: </b></span><b style="font-family: inherit; font-size: inherit; font-style: inherit; font-variant-ligatures: inherit; font-variant-caps: inherit;">[petsc-users]
obtaining estimated Hessian in BQNLS</b><br>
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<div style="margin:0px"><span style="font-family: -webkit-system-font, "Helvetica Neue", Helvetica, sans-serif; margin: 0px; color: black;"><b>Date:<span> </span></b></span><span style="margin:0px">April 25, 2023 at 4:15:35 AM EDT<br>
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<div style="margin:0px"><span style="font-family: -webkit-system-font, "Helvetica Neue", Helvetica, sans-serif; margin: 0px; color: black;"><b>To:<span> </span></b></span><span style="margin:0px">"petsc-users@mcs.anl.gov" <petsc-users@mcs.anl.gov><br>
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<div style="margin:0px"><span style="font-family: -webkit-system-font, "Helvetica Neue", Helvetica, sans-serif; margin: 0px; color: black;"><b>Message-Id:<span> </span></b></span><span style="margin:0px"><05357d86ee454f49a8499739c3654b3a@ICTS-S-EXMBX23.luna.kuleuven.be><br>
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<div style="font-size:11pt;font-family:Calibri, sans-serif;margin:0px"><span lang="en-US" style="margin:0px">Dear PETSc developers,</span></div>
<div style="font-size:11pt;font-family:Calibri, sans-serif;margin:0px"><span lang="en-US" style="margin:0px"> </span></div>
<div style="font-size:11pt;font-family:Calibri, sans-serif;margin:0px"><span lang="en-US" style="margin:0px">I’m using PETSc version 3.14.1 coupled to a Fortran code, and I was wondering if there is a way of obtaining in output, possibly at each iteration,
the estimated Hessian matrix for the BQNLS method.</span></div>
<div style="font-size:11pt;font-family:Calibri, sans-serif;margin:0px"><span lang="en-US" style="margin:0px"> </span></div>
<div style="font-size:11pt;font-family:Calibri, sans-serif;margin:0px"><span lang="en-US" style="margin:0px">Thank you in advance and best regards,</span></div>
<span style="font-size:11pt;font-family:Calibri, sans-serif;margin:0px"><span lang="en-US" style="margin:0px">Stefano Carli</span></span></div>
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