TeX source:

{q_m}(t) =\left\{ \begin{array}{lllllll} p_mt, & 0 ≤ t ≤ T_R \\ p_mT - iD_R, & iT_R < t ≤ (i+1) \quad i = 1, 2, ..., (r-1)\\ p_mT - rD_R, & rT_R < t ≤ T_s \\ p_m T_s - rD_r, & T_{s} < t ≤ (r+1) T_R \\ p_mT_s - iD_R, & iT_R < t ≤ (i+1) T_R \quad i = r+1, r+2, ..., (n-1)\\ p_m T_s - nD_R, &nT_R < t ≤ (n+1) T_R\\ 0, & (n+1)T_R < t ≤ T \end{array} \right.