Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!yale!zador-anthony
From: zador-anthony@CS.YALE.EDU (anthony zador)
Newsgroups: comp.lang.c
Subject: evaluating math w/o recompile
Message-ID: <72603@yale-celray.yale.UUCP>
Date: 14 Sep 89 17:35:26 GMT
References: <7598@goofy.megatest.UUCP> <34566@apple.Apple.COM> <556@tigger.planet.bt.co.uk> <451@siswat.UUCP>
Sender: root@yale.UUCP
Reply-To: zador-anthony@CS.YALE.EDU (anthony zador)
Organization: Yale University Computer Science Dept, New Haven CT  06520-2158
Lines: 42


 
I have functions of the form

double f(V,t) 
  double V,t;
{
  return (some math function involving about a 
       line of exp, division, mult and add
       on V, t)
}

I use these functions to construct a table:

Table(f, table_array)
   ptr_to_fun f;
   double_array table_array;
{
  construct table_array by evaluating f[n]
}
I would like to be able to specify the form of the function f
at *run time* (no recompiles). That is, i would like 
to place a line of math
in some file and have the program read it in and evaluate it.

For example, my fnct could be
    1.6/(1+exp(-0.072*(V-5.0)))
or 
   0.02*(V+8.69)/(exp((V+8.69)/5.36)-1)         



I have played around with "hoc", the high order calculator
described in the Unix Programming Environment by K&P, but that seems
like overkill for this task. Is there a simpler way?


I'd appreciate any ideas.

--Tony Zador
zador@yale-sun3-nebula.arpa 
zador@nebula.sun3.cs.yale.edu