Re: finite summation - how to call a function from parameter stack

[Hans-Bernhard B. <HBB...@t-...>]

On 11.01.2011 18:00, mw...@gm... wrote:

> I want to add finite summation to gnuplot, that is a function sum(a,
> b, x, f), where a, b (int) are the summation boundary, x (double) is
> a varialbe, f (string) is the name of the function to eveluate a
> term. Example usage:

Without changing gnuplot, one can already do this recursive function:

	sum_f(a,b,delta) = (a < b) ? 0 : (f(a) + sum_f(a+delta,b,delta))

For more tricky examples, see bivariat.dem

The only aspect of your job this doesn't cover is passing in a function 
as another function's argument.  gnuplot is a plotting program after 
all, not a full-fledged functional programming language.

I don't think adding 'sum' as a new builtin is worth the effort.  If a 
new builtin is to be added, then that should be an eval() function, i.e. 
a function that takes a string and treats it as an expression to 
evaluate, so the above could be expanded to

   sum(f,a,b,delta) = (a<b)?0 : (eval("f(a)")+sum_f(a+delta,b,delta))