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RfastOfficial / Rfast

A collection of Rfast functions for data analysis. Note 1: The vast majority of the functions accept matrices only, not data.frames. Note 2: Do not have matrices or vectors with have missing data (i.e NAs). We do no check about them and C++ internally transforms them into zeros (0), so you may get wrong results. Note 3: In general, make sure you give the correct input, in order to get the correct output. We do no checks and this is one of the many reasons we are fast.
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mat.mult produces wrong results #27

Closed linliu-stats closed 4 years ago

linliu-stats commented 4 years ago

While I'm trying to use mat.mult instead of %*% to do matrix multiplication, I get wrong results. Please see the following as an example:

library(Rfast) Loading required package: Rcpp Loading required package: RcppZiggurat a <- matrix(c(1,2,3,4,5,6),3,2) b <- matrix(c(1,2,3,4),2,2) mat.mult(a,b) [,1] [,2] [1,] 9 19 [2,] 12 26 a %*% b [,1] [,2] [1,] 11 23 [2,] 10 24 [3,] 14 30

What's interesting is that I don't have such a problem two months ago the last time I used mat.mult. Any help will be appreciated.

linliu-stats commented 4 years ago

Also, it seems that mat.mult changes the result from time to time...

a [,1] [,2] [1,] 1 4 [2,] 2 5 [3,] 3 6 b [,1] [,2] [1,] 1 3 [2,] 2 4 mat.mult(a, b) [,1] [,2] [1,] 9 19 [2,] 12 26 mat.mult(a, b) [,1] [,2] [1,] 11 23 [2,] 10 24 mat.mult(a, b) [,1] [,2] [1,] 7 15 [2,] 9 23 mat.mult(a, b) [,1] [,2] [1,] 5 11 [2,] 11 25 mat.mult(a, b) [,1] [,2] [1,] 9 19 [2,] 12 26

statlink commented 4 years ago

We know this is wrong and we will fix it. This mistake has been pointed out by other users as well.