code: @Override
      public INDArray getActivation(INDArray in, boolean training) {
          // no support in ELU native to override alpha
          if (this.alpha != 1.00) {
              INDArray alphaMultiple = Nd4j.getExecutioner().exec(new ELU(in.dup()));
              alphaMultiple.muli(alpha);
              BooleanIndexing.replaceWhere(in, alphaMultiple, Conditions.lessThan(0));
          } else {
              Nd4j.getExecutioner().execAndReturn(new ELU(in));
          }
          return in;
      }
docs: /*
  = alpha * (exp(x) - 1.0); x < 0
  f(x)
  = x ; x >= 0