Hello @futureRpro, welcome to RStudio Community.
From the documentation:
Arguments
y
NULL (default) or a vector, matrix or data frame with compatible dimensions to x. The default is equivalent to y = x (but more efficient).
So calling var() without specifying a y argument is equivalent to passing the same argument to both x and y.
m <- matrix(1:12, nrow = 4, byrow = FALSE)
n <- matrix(1:12, nrow = 4, byrow = FALSE)
var(x = m, y = n)
#> [,1] [,2] [,3]
#> [1,] 1.666667 1.666667 1.666667
#> [2,] 1.666667 1.666667 1.666667
#> [3,] 1.666667 1.666667 1.666667
Created on 2020-04-14 by the reprex package (v0.3.0)