Re: Order of operations (was: Eigenvalues &/or eigenvectors,
Re: Order of operations (was: Eigenvalues &/or eigenvectors,
- Subject: Re: Order of operations (was: Eigenvalues &/or eigenvectors,
- From: Nigel Garvey <email@hidden>
- Date: Thu, 8 May 2003 23:56:03 +0100
Deivy Petrescu wrote on Thu, 8 May 2003 12:42:35 -0400:
>
On Thursday, May 8, 2003, at 11:25 AM, Doug McNutt wrote:
>
>
> ... The problem is that some professor in some computer science
>
> department decided there was something called a "unary minus" operator
>
> which is not a subtraction. Back when algebra was taught in high
>
> school - remember that? - we learned that a leading minus sign implied
>
> a preceding zero.
Curiously, when changing the sign of a number held in an AppleScript
variable, an explicit subtraction from zero works slightly faster than
simply bunging a minus in front of the variable name. You have to do this
about half a million times for it to be noticeable but it's definitely
the case.
>
Something like this already happened at NASA! They mixed units, British
>
and SI. I can not remember what was it, but it was major...
It was one of the Mars missions - a lander and two piggy-back probes that
were supposed to detach on the way down and bury themselves in the ground
at different sites. The assembly went round the back of the planet during
its braking burn and was never heard of again. The enquiry found that
different companies had made different assumptions about the measuring
units to be used when calculating the required thrust.
>
I do not believe it was AS fault.
Mac OS X offers a choice of "standard" or metric measuring units, which
is the sort of unconscious arrogance that probably led to the loss of the
mission. (X also offers the choice of "British English", "Canadian
English", and "English" spelling dictionaries - but let that pass.) ;-)
NG
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