Fix boundary condition y-coordinate in Heat Conduction tutorial

Author: nikoscham

tutorials/HeatConduction2DFin.html

@@ -99,7 +99,7 @@ <h2 id="mathematicalformulation"><a name="Mathematical formulation"></a>Mathemat
       constant temperature boundary conditions are implemented as Dirichlet types in the finite element code.
       The symmetry boundary condition is implemented as a Neumann zero-flux type \( \left(
       \frac{dT}{dx}|_{x=0}=0 \right) \), while the convective cooling boundary condition is of the Robin type.
-      Specifically, the latter is expressed as \(\frac{dT}{dy}|_{y=4}=-{\frac{h}{k}}(T-T_0)\), where \(h\) is
+      Specifically, the latter is expressed as \(\frac{dT}{dy}|_{y=2}=-{\frac{h}{k}}(T-T_0)\), where \(h\) is
       the heat transfer coefficient, \(k\) the thermal conductivity and \(T_0\) is the external temperature.
       We assume here that \({\frac{h}{k}}\) = 1 m<sup>-1</sup> and \(T_0\) = 20 &deg;C.
     </p>