[R] Decimal Accuracy Loss?

Brigid Mooney bkmooney at gmail.com
Wed Apr 6 17:33:48 CEST 2011

This is hopefully a quick question on decimal accuracy.  Is any
decimal accuracy lost when casting a numeric vector as a matrix?  And
then again casting the result back to a numeric?

I'm finding that my calculation values are different when I run for
loops that manually calculate matrix multiplication as compared to
when I cast the vectors as matrices and multiply them using "%*%".
(The errors are very small, but the process is run iteratively
thousands of times, at which point the error between the two
differences becomes noticeable.)

I've read FAQ # 7.31 "Why doesn't R think these numbers are equal?",
but just want to confirm that the differences in values are due to
differences in the matrix multiplication operator and manual
calculation via for loops, rather than information that is lost when
casting a numeric as a matrix and back again.

Thanks in advance for the help,

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