Sollya User's Manual

Name:

isevaluable tests whether a function can be evaluated at a point

Usage:

isevaluable(function, constant) : (function, constant) -> boolean

Parameters:

function represents a function
constant represents a constant point

Description:

isevaluable applied to function function and a constant constant returns a boolean indicating whether or not a subsequent call to evaluate on the same function function and constant constant will produce a numerical result or NaN. This means isevaluable returns false iff evaluate will return NaN.
The command isevaluable is now considered DEPRECATED in Sollya. As checks for NaNs are now possible in Sollya, the command isevaluable can be fully emulated with a call to evaluate and a couple of tests, as shown below in the last example.

Example 1:

   > isevaluable(sin(pi * 1/x), 0.75);
   true
   > print(evaluate(sin(pi * 1/x), 0.75));
   -0.86602540378443864676372317075293618347140262690518

Example 2:

   > isevaluable(sin(pi * 1/x), 0.5);
   true
   > print(evaluate(sin(pi * 1/x), 0.5));
   [-1.72986452514381269516508615031098129542836767991679e-12715;7.5941198201187963145069564314525661706039084390067e-12716]

Example 3:

   > isevaluable(sin(pi * 1/x), 0);
   false
   > print(evaluate(sin(pi * 1/x), 0));
   [@NaN@;@NaN@]

Example 4:

   > procedure isEvaluableEmulation(f, c) {
       return match evaluate(f, c) with
               NaN : (false)
            [NaN;NaN] : (false)
            default : (true);
     };
   > isEvaluableEmulation(sin(pi * 1/x), 0.75);
   true
   > isEvaluableEmulation(sin(pi * 1/x), 0.5);
   true
   > isEvaluableEmulation(sin(pi * 1/x), 0);
   false