【提问】代码最后一句查了帮助还是不懂

eqns = {Flatten@
Table[{-I Derivative[1][u[i]][
t] == \[Beta]1 (u[i - 1][t] + u[i + 1][t])}, {i, 2, 19}],
-I Derivative[1][u[1]][t] == \[Beta]1 u[2][t],
-I Derivative[1][u[20]][t] == \[Beta]1 u[19][t],
Flatten@Table[{u[i][0] == 0}, {i, 1, 10}], u[11][0] == 1,
Flatten@Table[{u[i][0] == 0}, {i, 12, 20}]} /. {\[Beta]1 -> 0.5};
ans = NDSolve[eqns, Flatten@Table[{u[i]}, {i, 1, 20}], {t, 0, 10}];
Abs[u[1][5] /. ans[[1]] ]^2
前面两段是求解一系列微分方程，最后一句是干什么的？请好心人解答，谢谢！