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Why is datenummx(clock) faster than now()?

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Why is running datenummx(clock) 4x faster than the standard now() call? https://gist.github.com/4432190

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per isakson
per isakson on 2 Jan 2013
Edited: per isakson on 2 Jan 2013
The function, now, has one executable line of code
t = datenum(clock);
the function, datenum, calls the function, datenummx, after having done error checking, etc.
That's why.
  2 Comments
Dan Couture
Dan Couture on 3 Jan 2013
Thanks per isakson.
I did see the layers of function calls below now() which is where I dug out the datenummx(clock) code. My question was intended to focus on why does matlab have all those layers in between that just slow it down? My apologies for the vagueness of the originial question.
  • Why does Matlab not alias now() directly to datenummx(clock)?
  • There is no user input, so error checking should be minimal (if any)
and as a follow-up:
  • Is there something still below the datenummx call that would be even faster?
I am running a fairly complex simulation through object oriented m-files and need to reference the current system time quickly and continually.
per isakson
per isakson on 3 Jan 2013
Edited: per isakson on 3 Jan 2013
I often find it difficult to understand the rational behind various design decisions of The MathWorks (TMW). Since, TMW is successful in the money-making industry, I guess TMW knows what they are doing.
Regarding datenummx I guess it is possible to make a faster function (little error checking, one OS (Windows only), maybe "in-place".) Post a new question.

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