4. 对齐：把连续位置准确交给现有特征图 · 实现代码

# 独立一维采样练习；不等同于完整二维 RoIAlign。
import math
feature = [0.0,1.0,2.0,6.0,7.0]
stride = 16.0
for x in [32.0,35.0,36.0,40.0,48.0]:
    u = x/stride
    lo = math.floor(u); hi = min(lo+1,len(feature)-1)
    alpha = u-lo
    v = (1-alpha)*feature[lo]+alpha*feature[hi]
    print(f'原图x={x:g}, 特征u={u:g}, 左邻={lo}, 插值={v:g}')
assert math.isclose((1-0.1875)*2+0.1875*6,2.75)