https://svn.boost.org/trac10/ticket/6327 <p> The documentation under <a href="http://www.boost.org/doc/libs/1_48_0/libs/numeric/ublas/doc/triangular.htm#1TriangularMatrix">http://www.boost.org/doc/libs/1_48_0/libs/numeric/ublas/doc/triangular.htm#1TriangularMatrix</a> says in Section 1.1: </p> <p> <em>For a (n x n )-dimensional <strong>lower</strong> triangular matrix and 0 &lt;= i &lt; n,0 &lt;= j &lt; n holds ti, j = 0 , if i &gt; j. If furthermore holds ti, i= 1 the matrix is called unit <strong>lower</strong> triangular. For a (n x n )-dimensional lower triangular matrix and 0 &lt;= i &lt; n,0 &lt;= j &lt; n holds ti, j = 0 , if i &lt; j. If furthermore holds ti, i= 1 the matrix is called unit lower triangular.</em> </p> <p> Based on the code example in Section 1.2, I think that the bolded occurrences of "lower" should be replaced with "upper", so that the above paragraph reads: </p> <p> <em>For a (n x n )-dimensional <strong>upper</strong> triangular matrix and 0 &lt;= i &lt; n,0 &lt;= j &lt; n holds ti, j = 0 , if i &gt; j. If furthermore holds ti, i= 1 the matrix is called unit <strong>upper</strong> triangular. For a (n x n )-dimensional lower triangular matrix and 0 &lt;= i &lt; n,0 &lt;= j &lt; n holds ti, j = 0 , if i &lt; j. If furthermore holds ti, i= 1 the matrix is called unit lower triangular.</em> </p> en-us /htdocs/site/boost.png https://svn.boost.org/trac10/ticket/6327 Trac 1.4.3