ith a large number of example codes to illustrate usage. Here, we highlight a few, key ones:</h4>
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<ul>
  <li> <a href="#example1">Linear Poisson equation on a 2D grid</a>
    <ul>
      <li> example of linear equation problem </li>
      <li> see also <a href="https://www.mcs.anl.gov/petsc/petsc-current/src/ksp/