相同时间的位移差比例都是a，谁能给个s与t的公式哈，初始速度为v0
例如
a = 2时
t=0时 s0 = 0
t=1 时 s1 = 1, s1 - s0 = 1;
t=2时 s2 = 3 = s1 + a * (s1 - s0), s2 - s1 = 2;
t=3时 s3 = 7 = s2 + a * (s2 - s1), s3 - s2 =4;
t=4时 s4 = 15 = s3 + a * (s3 - s2) s4 - s3 = 8
t 是float型
s=2^t-1…
s=(a^t-1)/(a-1)