$$
\newcommand{\half}{\frac{1}{2}}
\newcommand{\tp}{\thinspace .}
\newcommand{\uex}{{u_{\small\mbox{e}}}}
\newcommand{\normalvec}{\boldsymbol{n}}
\newcommand{\x}{\boldsymbol{x}}
\newcommand{\X}{\boldsymbol{X}}
\renewcommand{\v}{\boldsymbol{v}}
\newcommand{\V}{\boldsymbol{V}}
\newcommand{\dfc}{\alpha}  % diffusion coefficient
\newcommand{\If}{\mathcal{I}_s}     % for FEM
\newcommand{\Ifb}{{I_b}}  % for FEM
\newcommand{\sequencei}[1]{\left\{ {#1}_i \right\}_{i\in\If}}
\newcommand{\sequencej}[1]{\left\{ {#1}_j \right\}_{j\in\If}}
\newcommand{\basphi}{\varphi}
\newcommand{\baspsi}{\psi}
\newcommand{\refphi}{\tilde\basphi}
\newcommand{\sinL}[1]{\sin\left((#1+1)\pi\frac{x}{L}\right)}
\newcommand{\xno}[1]{x_{#1}}
\newcommand{\yno}[1]{y_{#1}}
\newcommand{\dX}{\, \mathrm{d}X}
\newcommand{\dx}{\, \mathrm{d}x}
\newcommand{\ds}{\, \mathrm{d}s}
\newcommand{\Real}{\mathbb{R}}
$$
    
Bibliography 
 -   H. P. Langtangen. 
    Approximation of functions,
    http://tinyurl.com/k3sdbuv/pub/approx.
 
 -   M. G. Larson and F. Bengzon. 
    The Finite Element Method: Theory, Implementation, and Applications,
    Texts in Computational Science and Engineering,
    Springer,
    2013.
 
 -   D. Braess. 
    Finite Elements: Theory, Fast Solvers, and Applications in Solid Mechanics,
    third edition,
    Cambridge University Press,
    2007.
 
 -   S. Brenner and R. Scott. 
    The Mathematical Theory of Finite Element Methods,
    third edition,
    Springer,
    2007.
 
 -   C. Johnson. 
    Numerical Solution of Partial Differential Equations by the Finite Element Method,
    Dover,
    2009.
 
 -   K. Eriksson, D. Estep, P. Hansbo and C. Johnson. 
    Computational Differential Equations,
    second edition,
    Cambridge University Press,
    1996.
 
 -   A. Quarteroni and A. Valli. 
    Numerical Approximation of Partial Differential Equations,
    Springer,
    1994.