[R] converting MATLAB -> R | element-wise operation

[Evan Cooch]

So, trying to convert a very long, somewhat technical bit of lin alg 
MATLAB code to R. Most of it working, but raninto a stumbling block that 
is probaably simple enough for someone to explain.

Basically, trying to 'line up' MATLAB results from an element-wise 
division of a matrix by a vector with R output.

Here is a simplified version of the MATLAB code I'm translating:

NN = [1, 2, 3; 4, 5, 6];  % Example matrix
lambda = [2, 3, 4];  % Example vector
result_matlab = NN ./ lambda;

which yields

  0.50000   0.66667   0.75000
  2.00000   1.66667   1.50000


So, the only way I have stumbled onto in R to generate the same results 
is to use 'sweep'. The following 'works', but I'm hoping someone can 
explain why I need something as convoluted as this seems (to me, at least).

NN <- matrix(c(1, 2, 3, 4, 5, 6), nrow = 2, byrow = TRUE)  # Example matrix
lambda <- c(2, 3, 4)  # Example vector
sweep(NN, 2, lambda, "/")


      [,1]      [,2] [,3]
[1,]  0.5 0.6666667 0.75
[2,]  2.0 1.6666667 1.50

First tried the more 'obvious' NN/lambda, but that yields 'the wrong 
answer' (based solely on what I'm trying to accomplish):


        [,1] [,2] [,3]
[1,] 0.500000  0.5  1.0
[2,] 1.333333  2.5  1.5

So, why 'sweep'?

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