<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html > <head><title></title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <meta name="generator" content="TeX4ht (http://www.tug.org/tex4ht/)"> <meta name="originator" content="TeX4ht (http://www.tug.org/tex4ht/)"> <!-- html,3 --> <meta name="src" content="userhtml.tex"> <link rel="stylesheet" type="text/css" href="userhtml.css"> </head><body > <div class="footnote-text"> <!--l. 195--><p class="noindent" ><span class="footnote-mark"><a id="fn2x0"> <sup class="textsuperscript">2</sup></a></span><span class="cmr-8">This is the normal situation when the pattern of the sparse matrix is symmetric, which is</span> <span class="cmr-8">equivalent to say that the interaction between two variables is reciprocal. If the matrix pattern is</span> <span class="cmr-8">non-symmetric we may have one-way interactions, and these could cause a situation in which a</span> <span class="cmr-8">boundary point is not a halo point for its neighbour.</span></div> </body></html>