elu method
Implementation
Value elu(double alpha) {
final out = data >= 0
? Value(data, {this}, 'ELU')
: Value(alpha * (math.exp(data) - 1), {this}, 'ELU');
out._backward = () {
grad += (out.data >= 0 ? 1.0 : alpha * math.exp(data)) * out.grad;
};
return out;
}