Add links to step-20 and 22.

diff --git a/examples/step-20/doc/intro.dox b/examples/step-20/doc/intro.dox
index 49ebe139095b0f29a4eb9f5dca75dd2147d0dcd3..bda18d18e11690ad923ba64908754fbb5e2bf0c1 100644 (file)
--- a/examples/step-20/doc/intro.dox
+++ b/examples/step-20/doc/intro.dox
@@ -124,8 +124,12 @@ space $H({\textrm{div}})=\{{\mathbf w}\in L^2(\Omega)^d:\ {\textrm{div}}\ {\math
 for $\mathbf u$,$\mathbf v$, and $L^2$ for $p,q$. It is a well-known fact stated in
 almost every book on finite element theory that if one chooses discrete finite
 element spaces for the approximation of ${\mathbf u},p$ inappropriately, then the
-resulting discrete saddle-point problem is instable and the discrete solution
-will not converge to the exact solution.
+resulting discrete problem is instable and the discrete solution
+will not converge to the exact solution. (Some details on the problem
+considered here -- which falls in the class of "saddle-point problems"
+-- can be found on the Wikipedia page on the <a
+href="https://en.wikipedia.org/wiki/Ladyzhenskaya%E2%80%93Babu%C5%A1ka%E2%80%93Brezzi_condition">Ladyzhenskaya-Babuska-Brezzi
+(LBB) condition</a>.)
 
 To overcome this, a number of different finite element pairs for ${\mathbf u},p$
 have been developed that lead to a stable discrete problem. One such pair is

diff --git a/examples/step-22/doc/intro.dox b/examples/step-22/doc/intro.dox
index f8f5664ffa88c34b88b2817dd3a93950597bdb02..b62dd66ebfe6ab8f6da73589734084233b102a56 100644 (file)
--- a/examples/step-22/doc/intro.dox
+++ b/examples/step-22/doc/intro.dox
@@ -351,11 +351,13 @@ for all test functions
 $\textbf{v}\in \textbf V_0 = \{\varphi \in H^1(\Omega)^d: \varphi_{\Gamma_D}=0\},q\in
 Q$.
 
-These equations represent a symmetric saddle point problem. It is well known
+These equations represent a symmetric <a
+href="https://en.wikipedia.org/wiki/Ladyzhenskaya%E2%80%93Babu%C5%A1ka%E2%80%93Brezzi_condition">saddle
+point problem</a>. It is well known
 that then a solution only exists if the function spaces in which we search for
 a solution have to satisfy certain conditions, typically referred to as the
 Babuska-Brezzi or Ladyzhenskaya-Babuska-Brezzi (LBB) conditions. The continuous
-function spaces above satisfy them. However, when we discretize the equations by
+function spaces above satisfy these. However, when we discretize the equations by
 replacing the continuous variables and test functions by finite element
 functions in finite dimensional spaces $\textbf V_{g,h}\subset \textbf V_g,
 Q_h\subset Q$, we have to make sure that $\textbf V_h,Q_h$ also satisfy the LBB