I have a matrix of dimension n*k and I am trying to calculate another matrix which has all the pairs which will have n(n-1)/2 rows and k columns
New columns are element-wise multiplication of two different individual rows.
Below is the code,how i am calculating it currently:
mat = matrix(rnorm(10000,mean = 0,sd = 1), nrow = 100, ncol = 100) # n = 100, k = 100
mat2 = matrix(data = NA, nrow = nrow(mat)*(nrow(mat)-1)/2, ncol = ncol(mat))
counter = 0
for(i in seq(nrow(mat))){
# print(paste('i', i))
for(j in seq(nrow(mat))){
# print(paste('j', j))
if((i!= j)&(i<j)){
x = mat[i,]*mat[j,]
# print(x)
mat2 = rbind(mat2, x)
counter = counter + 1
print(paste('Counter - ', counter,' : Pair(', i,',', j, ')', sep = ''))
}
}
}
Its very brute force approach though with O(n^2). Is there a way to do the same computation with less time ?
