[R] Decimal Accuracy Loss?

From: Brigid Mooney <bkmooney_at_gmail.com>
Date: Wed, 06 Apr 2011 11:33:48 -0400


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,
Brigid



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