Given the following statements about a function f
\begin{itemize}
\item $\mathrm { f } ^ { \prime \prime } ( x ) = a$ for all $x$
\item $\mathrm { f } ( 0 ) = 1 , \mathrm { f } ( 1 ) = 2$
\item $\int _ { 0 } ^ { 1 } \mathrm { f } ( x ) \mathrm { d } x = 1$
\end{itemize}
find the value of $a$.