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You can refer to the example src/ts/tutorials/advection-diffusion-reaction/ex5adj_mf.c
<div class="">which uses a matrix-free approach for a 2D multi-component reaction-diffusion PDE. </div>
<div class="">In particular, you only need to look at MyIMatMult() and ignore the transposed version</div>
<div class="">which is intended for adjoint calculations.</div>
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<div class="">Hong (Mr.) <br class="">
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<div class="">On Sep 6, 2022, at 10:00 PM, Tu, Jiannan <<a href="mailto:Jiannan_Tu@uml.edu" class="">Jiannan_Tu@uml.edu</a>> wrote:</div>
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<span style="font-size: 12pt;" class="">I am using TS IMEX to solve a large DAE system. The DAE is obtained by applying finite FV method to 3-D multi-specie ion/neutral fluids equations with magnetic induction equation. The Jacobian for stiff part is formed
by using MatSetValuesStencil(). The Jacobian matrix is very sparse, no more than 10 non-zeros on each row. MatSetValuesStencil requires local to global mapping by calling ISLocaltoGlobalMapping(). Could you please instruct me how to use local to global mapping?<span class="Apple-converted-space"> </span><o:p class=""></o:p></span></div>
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<span style="font-size: 12pt;" class=""><o:p class=""> </o:p></span></div>
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<span style="font-size: 12pt;" class="">I also tried using DMCreateMatrix() to create the Jacobian. While local to global mapping is not necessary, the matrix takes too much memory and requires 64-bit indices. I would prefer to take the advantage of sparsity
of the Jacobian, pre-allocate the matrix to use as less as possible memory so that the code can be run on a multi-core desktop.<o:p class=""></o:p></span></div>
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<span style="font-size: 12pt;" class=""><o:p class=""> </o:p></span></div>
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<span style="font-size: 12pt;" class="">Thank you very much for your advice.<o:p class=""></o:p></span></div>
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<span style="font-size: 12pt;" class=""><o:p class=""> </o:p></span></div>
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<span style="font-size: 12pt;" class="">Jiannan</span></div>
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