decomposition is used to convert a fraction with multiple factors in the denominator into a sum of terms, with one
term for each factor and a constant in the numerator. Doing so simplifies integration and differentiation.
Note: If poles of X (t) are of multiple order, then
include a term for each order; i.e., if (t-1)2 is in the denominator (a pole), then include both (t-1)
and (t-2)2 terms.