[R] Matrix multiplication in R is inaccurate!!

[Uwe Ligges]

Vikas Rawal wrote:
> If you multiply a matrix by its inverse you should get an identity matrix. In R, you get an answer that is accurate up to about 16 decimal points? Why can't one get a perfect answer?

Because R makes use of a digital computer which cannot work exactly 
using floating-point arithmetics ...
Please read some textbook about a numerics and computers.

Uwe Ligges


> See for example: 
> 
> c(5,3)->x1
> c(3,2)->x2
> cbind(x1,x2)->x
> solve(x)->y
> x%*%y
> 
> Vikas Rawal
> 
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