private static IComplexNumber sigmoidDeriv(IComplexNumber number) {
double arg = number.complexArgument().doubleValue();
double sigArg = 1 / 1 + (FastMath.exp(-arg)) - 1 + .5f;
double ret = Math.exp(sigArg);
IComplexDouble sigmoid = Nd4j.createDouble(ret, 0);
IComplexNumber oneMinus = Nd4j.createComplexNumber(1, 1).subi(sigmoid);
return sigmoid.mul(oneMinus);
}
