For any real number x, let $[ \mathrm { x } ]$ denote the largest integer less than or equal to x. Let $f$ be a real valued function defined on the interval $[ - 10,10 ]$ by
$$f ( x ) = \left\{ \begin{array} { c c } x - [ x ] & \text { if } [ x ] \text { is odd } \\ 1 + [ x ] - x & \text { if } [ x ] \text { is even } \end{array} \right.$$
Then the value of $\frac { \pi ^ { 2 } } { 10 } \int _ { - 10 } ^ { 10 } f ( x ) \cos \pi x \, d x$ is