Re: Unit conversions and symbolic mathematics with Babel

[Alan Schmitt <alan.schmitt@polytechnique.org>]

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On 2014-09-03 08:54, dieter@duenenhof-wilhelm.de (H. Dieter Wilhelm) writes:

>   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?

It seems that you could use block chaining. Here is an extract of some
code I use to compute stats for my book keeping:

#+name: monthly_average
#+begin_src emacs-lisp :var starty=2014 :var startm=3 :var amount=100 
  (let* ((tm (decode-time))
         (cmonth (nth 4 tm))
         (cyear (nth 5 tm))
         (nbmonths (+ (* 12 (- cyear starty)) (- cmonth startm))))
    (calc-eval "round($ / $$, 2)" nil amount nbmonths))
#+end_src

#+name: ledger_average
#+begin_src emacs-lisp :var b="Quotidien" :var sy=2014 :var sm=3  :var sd="2014-03-01" :var p="Expenses:"
  (let* ((per (format "from %d-%d-01 to this month" sy sm))
         (a (org-sbe call_ledger (bucket (eval b)) (prefix (eval p)) (period (eval per)))))
    (org-sbe monthly_average (amount (eval a)) (starty (eval sy)) (startm (eval sm))))
#+end_src

The last line of the second block calls the first block to do its
computation. The first block does not have to be in emacs-lisp, but
I don't know calc well enough to do it directly in calc.

Best,

Alan

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