Re: Dimensions (was: What's the difference between...)

[cis.ohio-state.edu!zaphod.mps.ohio-state.edu!howland.reston.ans.net!agate !linus!linus.mitre.org!vgiddings-mac.mitre.org!user@ucbvax.Berkeley.EDU (Victo r Giddings)]

In article <1993Feb15.151209.7531@inmet.camb.inmet.com>,
stt@spock.camb.inmet.com (Tucker Taft) replies to:

In article <1993Feb13.232516.5229@seas.gwu.edu> 
   mfeldman@seas.gwu.edu (Michael Feldman) comments on support for
dimensional types:

> [discussion deleted}

One aspect of this problem that hasn't been mentioned and may greatly
affect the 
efficacy of some of the proposed solutions is that integer exponents aren't
enough!  At least some problems require that halves be expressable.

One of the first subprograms that I attempted to write (after the standard
one week "Intro to Ada" course) was Gauss's solution to the orbital
intercept problem.  In orbital mechanics,  the constant 1/SQRT(GM) occurs
fairly frequently.   The units of this quantity are sec/(km**3/2) !!  The
resulting package to define all the permutations of "unitary operations"
was so daunting that I reversed myself on advocating this type of checking.
 It requires support for SQRT in addition to "+", "-", "*", and "/".  I
commend the Gaussian intercept solution as a test case to those proposing
solutions for dimensional types.