exp

import std.math;
// f(x) = exp(x), f'(x) = exp(x)
auto x = dual(5.0, 1.0);
auto res = x.exp();
assert(approxEqual(res.re, std.math.exp(5.0)));
assert(approxEqual(res.du, std.math.exp(5.0)));

// f(x) = exp(3x), f'(x) = 3*exp(3x)
res = exp(3 * x);
assert(approxEqual(res.re, std.math.exp(15.0)));
assert(approxEqual(res.du, 3 * std.math.exp(15.0)));