note about removing diagonal of sparse matrix

Former-commit-id: 9990af95525814d0a140e3c098fb5ffaf8a8f5f9

matlab-to-eigen.html

@@ -279,6 +279,12 @@ bool a = A.array().any();
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+      <tr class=d0>
+        <td><pre><code>A = A - diag(diag(A));</code></pre></td>
+        <td><pre><code>A.prune([](const int r, const int c, const Scalar)-&gt;bool{return r!=c;});</code></pre></td>
+        <td>Remove the diagonal from a sparse matrix.</td>
+      </tr>
+
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