Re: [boost] Re: physical-quantities

From: Matthias Schabel (boost_at_[hidden])
Date: 2004-01-09 13:47:03

> Phil Richards wrote:
>> require that either "fahrenheit(32) + fahrenheit(32) ==  
>> fahrenheit(32)" or
>> "celsius(0) + celsius(0) == celsius(0)"
>
> Hmmm... does adding temperatures make sense in the first place...?...

This absolute vs. relative quantity issues arises pretty much  
everywhere.  For example,
if I have two points along the x-axis, one at 7 meters and another at  
12 meters, what does
it mean to add the two?  Nothing really.  We can add an increment in  
distance to either one,
to get a new absolute position or we could add two increments to get  
another increment, but
adding two absolute quantities doesn't really make sense.  In the same  
way, if I write

32*_fahrenheit+32*_fahrenheit = 64*_fahrenheit

it makes perfect sense if one or both of the terms on the left is a  
relative quantity, but not
if both are absolutes...

------------------------------------------------------------------------ 
---------------------------
Matthias Schabel, Ph.D.                           	
Utah Center for Advanced Imaging Research
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mschabel at ucair med utah edu