[R] Change of sign with division by zero, i.e. -1/0 = Inf ??

[Cesar Caballero]

Hi R-users,

I am facing a strange behaviour that changes the sign of Inf with a division by zero.

In my script, I have defined the following 3 variables and the elementwise division:

> lambda_k[gamma_lambda]  # numeric vector
[1] -1  0
> del_lambda[gamma_lambda] # numeric vector
[1]  0 -1
> gamma_lambda  # integer vector with the indexes of the elements in lambda_k & del_lambda
[1] 74 11
> lambda_k[gamma_lambda] / del_lambda[gamma_lambda]
[1] Inf   0

The result is surprising instead of -Inf 0 which I would expect because the elementwise division of the elements with index 74 is -1/0.


Surprisingly, if I try to do the division with just newly defined numeric vectors with the same values, I obtain the correct result, i.e.
> c(-1,0) / c(0,-1)
[1] -Inf    0 


How can this be explained? Any input would be really welcomed.

For your information, I'm using R version 3.0.2 (2013-09-25) and Rstudio Version 0.98.501 on Platform: x86_64-apple-darwin10.8.0 (64-bit).


Thanks very much for your help,

Cesar

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Cesar Caballero
www.bcbl.eu 

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