<div class="highlight highlight-source-julia notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="A = sprand(100,100,0.1); A = A'*A;
A = A + im*speye(100);
b = randn(100);
x = A\b
Error code -4 from numeric factorization"><pre class="notranslate">A <span class="pl-k">=</span> <span class="pl-c1">sprand</span>(<span class="pl-c1">100</span>,<span class="pl-c1">100</span>,<span class="pl-c1">0.1</span>); A <span class="pl-k">=</span> A<span class="pl-k">'</span><span class="pl-k">*</span>A;
A <span class="pl-k">=</span> A <span class="pl-k">+</span> im<span class="pl-k">*</span><span class="pl-c1">speye</span>(<span class="pl-c1">100</span>);
b <span class="pl-k">=</span> <span class="pl-c1">randn</span>(<span class="pl-c1">100</span>);
x <span class="pl-k">=</span> A<span class="pl-k">\</span>b
Error code <span class="pl-k">-</span><span class="pl-c1">4</span> from numeric factorization</pre></div>
<p dir="auto">This type of systems are very important to many problems in electrical engineering and geoscience</p>
<p dir="auto">[jiahao: edit for code formatting]</p>
<p dir="auto">A simple example:</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content=" M = speye(2) + im * speye(2);
 lufact(M);
 ERROR: Error code -4 from numeric factorization
  in error at error.jl:21
  in umfpack_numeric! at linalg/umfpack.jl:159"><pre class="notranslate"><code class="notranslate"> M = speye(2) + im * speye(2);
 lufact(M);
 ERROR: Error code -4 from numeric factorization
  in error at error.jl:21
  in umfpack_numeric! at linalg/umfpack.jl:159
</code></pre></div>
<p dir="auto">Sparse real matrices and complex full matrices work fine.</p>