On 10/24/07, Frank Hamilton <[EMAIL PROTECTED]> wrote:
> Has anyone considered an application to calculate with systems of
> units, such as SI?
Here's an attempt at tracking dimensions:
units=:3 :0"0&;:
assert._1-:nc y ['new unit name must have no other meaning'
L1=. 'assert.0=#$0+n [''unit exponent must be scalar'''
L2=. '(;:''',(>y),''');m,&<n'
(y)=: 2 :(L1;L2)
i.0 0
)
uni=:1 :0
:
'xu xv xx'=.x
'yu yv yx'=.y
zv=.xv u yv NB. basic operation
xb=.xu e.yu NB. find unit overlap
select. u`''
case. +`'' do.
assert. xu -: yu ['units must match'
assert. xx -: yx ['unit exponents must match'
zu=. xu
zx=. xx
NB. repeat for -
case. *`'' do.
zu=. ~.xu,yu
zx=. (xu,yu) +//. xx,yx
case. %`'' do.
zu=. ~.xu,yu
zx=. (xu,yu) -//. xx,yx
case. do. assert 0['unsuppported operation'
end.
(/:~zu);zv ,&< zx/:zu
)
raw=: 1 {:: ]
example use:
units 'm g s' NB. meters grams seconds
10 m 1 NB. 10 meters
10 m 1 *uni 10 s _1 NB. meters/second
10 m 1 *uni 10 s _1 * uni 10 s _1 NB. meters/second^2
Notes:
I have performed only very limited testing
I do not currently support subtraction -- see coment in uni for how
to fix that. I think select should be modified to support multiple
case. entries with a single do. but I guess I should post that on
the wiki feature request page.
units must be declared exactly once. In a script, I recommend
preceding units with erase. For example:
erase 'm g s'
units 'm g s'
If you prefer, erase y could be incorporated in the body of units
All manipulations of numbers must either use uni operations or
raw values.
--
Raul
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
