相关疑难解决方法(0)

给定x长度为k 的向量,我想通过k矩阵获得ak,X其中X[i,j]是k 的总和x[i] + ... + x[j].我现在这样做的方式是

set.seed(1)
x <- rnorm(10)

X <- matrix(0,10,10)
for(i in 1:10) 
  for(j in 1:10)
    X[i,j] <- sum(x[i:j])

#             [,1]       [,2]       [,3]      [,4]        [,5]       [,6]        [,7]      [,8]      [,9]      [,10]
# [1,]  -0.6264538 -0.4428105 -1.2784391 0.3168417  0.64634948 -0.1741189  0.31331014 1.0516348 1.6274162  1.3220278
# [2,]  -0.4428105  0.1836433 -0.6519853 0.9432955  1.27280329  0.4523349  0.93976395 1.6780887 2.2538700  1.9484816
# [3,]  -1.2784391 -0.6519853 -0.8356286 0.7596522  1.08915996  0.2686916  0.75612063 1.4944453 2.0702267  1.7648383
# [4,] …