Re: Unit conversions and symbolic mathematics with Babel

[Eric Abrahamsen <eric@ericabrahamsen.net>]

dieter@duenenhof-wilhelm.de (H. Dieter Wilhelm) writes:

> Hello Org,
>
> for some engineering most often I need estimations with unit
> conversions, Emacs Calc is perfect for this.
>
> When it comes to reporting and documentation I'd like to do it with
> org-mode, of course.  For numerical stuff and visualisation purposes I'm
> using already R and TikZ. But for unit conversions and symbolic maths
> I'm in a bind when trying to do this with free programs.

If you're on a linux of some sort, you probably have the "units" command
line program installed. That's sort of the mother of all unit
converters, as far as I'm concerned -- you could call out to it and
return the results. What do you think?

> - R :: Do you have experience with a units packages under the R-project?
>   What I've seen so far is not so reassuring...
>
> - Maxima :: I think there is a nice and intuitive units package for
>   maxima.  But this would mean learning an additional tool and mentally
>   switching between both within one document.
>
> - Calc :: I'd prefer to do it with Calc but the Babel interface is
>   (yet?) restricted
>
>   For example, I can define functions and do some unit conversions:
>
>     #+BEGIN_SRC emacs-lisp
>     (defmath cvun(a b)
> 	  (math-convert-units a b))
>     #+END_SRC
>
>
>     #+RESULTS:
>     : calcFunc-cvun
>
>     #+BEGIN_SRC calc :var L1 = "5 mm" 
>     cvun( L1, m)
>     #+END_SRC    
>
>
>     #+RESULTS:
>     : 5e-3 m
>
>   But what is missing is to assign variables within a source block
>   
>
>     #+BEGIN_SRC calc :var L1 = "5 mm" 
>     L2 := cvun( L1, m)
>     #+END_SRC    
>
>   
>   Unfortunately this is not working.  Do you have an idea how to
>   implement this?
>
> - Are you using (better) alternatives?
>
> Thanks for your insights
>
>        Dieter