finite summation - how to call a function from parameter stack

[<mw...@gm...>]

Hi,

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:

f(n, x) = sin(n*x)
plot sum(1, 10, x, "f")

I am stuck at how to call f from sum (see call(f) below) and would appreciate your help very much. (I assume f is the string representing the name of the function to call.)

-    for (i=a; i<=b; ++i) {
-        // calculate f_i(x);
-        push(Gcomplex(&tmp, x.real, x.imag)); // todo check the order
-        push(Ginteger(&tmp, i));
-
-        //call(f); // assume f is the name (string) of the function to call
-
-        pop(&tmp);
-        ret.real += real(&tmp);
-        ret.imag += imag(&tmp);
-    }

Thank you very much for your time and effort.

--- specfun.c   2011-01-11 17:40:19.000000000 +0100
+++ specfun.c.orig  2011-01-11 17:37:27.000000000 +0100
@@ -1933,44 +1933,3 @@
     push(Gcomplex(&a, x, 0.0));
 }
 
-void
-f_sum(union argument *arg)
-{
-    struct value tmp;
-    int a, b;
-    struct cmplx x, ret, result;
-    int i;
-
-    (void) arg;                        /* avoid -Wunused warning */
-
-    // pop x
-    pop(&tmp);
-    x.real = real(&tmp);
-    x.imag = imag(&tmp);
-
-    // pop b
-    if (pop(&tmp)->type != INTGR)
-        int_warn(NO_CARET, "expecting an integer as second argument to sum");
-    b = tmp.v.int_val;
-
-    // pop a
-    if (pop(&tmp)->type != INTGR)
-        int_warn(NO_CARET, "expecting an integer as first argument to sum");
-    a = tmp.v.int_val;
-    
-    ret.real = 0;
-    ret.imag = 0;
-    for (i=a; i<=b; ++i) {
-        // calculate f_i(x);
-        push(Gcomplex(&tmp, x.real, x.imag)); // todo check the order
-        push(Ginteger(&tmp, i));
-
-        //call(f);
-
-        pop(&tmp);
-        ret.real += real(&tmp);
-        ret.imag += imag(&tmp);
-    }
-
-    push(Gcomplex(&tmp, ret.real, ret.imag));
-}

--- eval.c  2011-01-11 16:25:01.000000000 +0100
+++ eval.c.orig 2011-01-11 17:38:00.000000000 +0100
@@ -176,8 +176,6 @@
     {"atanh",  f_atanh},
     {"lambertw",  f_lambertw}, /* HBB, from G.Kuhnle 20001107 */
 
-    {"sum",  f_sum}, /* summation */
-
     {"column",  f_column}, /* for using */
     {"valid",  f_valid},   /* for using */
     {"timecolumn",  f_timecolumn}, /* for using */
--- specfun.h   2011-01-11 16:22:05.000000000 +0100
+++ specfun.h.orig  2011-01-11 17:37:21.000000000 +0100
@@ -61,6 +61,4 @@
 void f_inverse_erf __PROTO((union argument *x));
 void f_lambertw __PROTO((union argument *x));
 
-void f_sum __PROTO((union argument *x));
-
 #endif /* GNUPLOT_SPECFUN_H */

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