<filename>slides/time_dependent_expression_variant_2.tex
\begin{frame}[fragile]
  \frametitle{Handling time-dependent expressions}
  \vspace{1em}
  We need to define a time-dependent expression for the boundary value:
{\tiny
  \begin{python}
# Start time
t0 = 0
g = Expression("exp(-4*DOLFIN_PI*DOLFIN_PI*t) \
               *cos(2*DOLFIN_PI*x[0]) \
               *cos(2*DOLFIN_PI*x[1])", t=t0, degree=3)

f = Expression("4*DOLFIN_PI*DOLFIN_PI \
        *exp(-4*DOLFIN_PI*DOLFIN_PI*t)\
        *cos(2*DOLFIN_PI*x[0]) \
        *cos(2*DOLFIN_PI*x[1])",t=t0, degree=3)
  \end{python}
}

Updating parameter values:
\vspace{-1em}
  \begin{python}
g.t = t
f.t = t
  \end{python}
\end{frame}
