void positive_jump_impl(RngBase& rng, double& value, const double scale) {
double new_value;
do {
new_value = value + rng.normal() * scale;
} while (new_value < 0);
value = new_value;
}
void jump_impl(RngBase& rng, double& value, const double scale) {
value += rng.normal() * scale;
}
void jump_impl(RngBase& rng, T& value, const double scale) {
for(size_t i = 0; i < value.n_elem; i++) {
value[i] += rng.normal() * scale;
}
}
// needed for completeness
void jump_impl(RngBase& rng, int& value, const double scale) {
value += lrint(rng.normal() * scale);
}