The command externalplot plots the error of an external function
evaluation code sequence implemented in the object file named
filename with regard to the function function. If mode
evaluates to absolute, the difference of both functions is
considered as an error function; if mode evaluates to relative,
the difference is divided by the function function. The resulting
error function is plotted on all floating-point numbers with
precision significant mantissa bits in the range range.
If the sixth argument of the command externalplot is given and evaluates to
perturb, each of the floating-point numbers the function is evaluated at gets perturbed by a
random value that is uniformly distributed in +/-1 ulp
around the original precision bit floating-point variable.
If a sixth and seventh argument, respectively a seventh and eighth
argument in the presence of perturb as a sixth argument, are given
that evaluate to a variable of type file|postscript|postscriptfile respectively to a
character sequence of type string, externalplot will plot
(additionally) to a file in the same way as the command plot
does. See plot for details.
The external function evaluation code given in the object file name
filename is supposed to define a function name f as
follows (here in C syntax): void f(mpfr_t rop, mpfr_t op).
This function is supposed to evaluate op with an accuracy corresponding
to the precision of rop and assign this value to
rop.