Improve the step-11 quadrature order explanation.

This little commit fixes three little issues with this paragraph:
1. A Gauss quadrature rule has order 2 r - 1 for r points, not 2 r + 1
2. p and p + 1 should be surrounded by $s
3. @>= should be replaced by the TeX command \geq

diff --git a/examples/step-11/step-11.cc b/examples/step-11/step-11.cc
index 7ef0f3a1dfe8790d7c8fd71e16dc1ac0f1532bfa..4f0d19abf320b7b3e641b6851fa19ca83655a739 100644 (file)
--- a/examples/step-11/step-11.cc
+++ b/examples/step-11/step-11.cc
@@ -298,11 +298,11 @@ namespace Step11
     // integrate over bilinear shape functions, so we know that we have to use
     // at least an order two Gauss quadrature formula. On the other hand, we
     // want the quadrature rule to have at least the order of the boundary
-    // approximation. Since the order of Gauss rule with $r$ points is $2r +
+    // approximation. Since the order of Gauss rule with $r$ points is $2r -
     // 1$, and the order of the boundary approximation using polynomials of
-    // degree p is p+1, we know that $2r@>=p$. Since r has to be an integer
-    // and (as mentioned above) has to be at least 2, this makes up for the
-    // formula above computing <code>gauss_degree</code>.
+    // degree $p$ is $p+1$, we know that $2r \geq p$. Since r has to be an
+    // integer and (as mentioned above) has to be at least $2$, this makes up
+    // for the formula above computing <code>gauss_degree</code>.
     //
     // Since the generation of the body force contributions to the right hand
     // side vector was so simple, we do that all over again for the boundary