Asymmetric cost function in neural networks I am trying to build a deep neural network based on asymmetric loss functions that penalizes underestimation of a time series. Preferably, by the use of the LINEX loss function (Varian 1975):
    $   \quad \quad 
L_{a,b}(y,\hat{y}) = b(e^{-a(y-\hat{y})} + a(y-\hat{y}) - 1), \quad \quad \quad \text{with } a \neq 0 \text{ and } b>0
$
but I can't find any research papers where this is done, and only very few on other asymmetric loss functions as well. 
The function is differentiable and gives reasonable results for values of a $\approx0$ using neuralnet(), for which the loss function approximates a square error function, but very poor results for increasing values of a.
This might explain why there are not many papers on asymmetric loss functions in neural networks, but why does it perform so bad when the asymmetry becomes larger? 
EDIT
With asymmetric loss functions, I mean loss functions that are biased and with different slopes for negative and positive error. Examples are given below.
 
Concerning my network: 
I used the neuralnet() package testing several options with 1 hidden layer for both sigmoid and tanh activation functions. At the end I used an identity function. At the LINEX loss function stated above, y is the desired output and $\hat{y}$ the activation output from the network. I have min-max normalized all 8 inputs as well as outputs y.
With the statement 

if a$\approx$0, the loss function approximates a square error function 
  I mean that the form of the LINEX loss function looks similar to a squared error function (symmetric), see picture below for example of LINEX loss wih b = 1 and a = 0.001
  

To restate my question: is there more research known that works with asymmetric loss functions in neural networks (preferably the LINEX)? If not, why? Since it is widely used for other model types.  
 A: 
This might explain why there are not many papers on asymmetric loss functions.

That's not true. Cross-entropy is used as loss function in most classification problems (and problems that aren't standard classification, like for example autoencoder training and segmentation problems), and it's not symmetric.
A: It's not correct that there are few papers that use an asymmetric loss function.  For instance, the cross-entropy loss is asymmetric, and there are gazillions of papers that use neural networks with a cross-entropy loss.  Same for the hinge loss.
It's not correct that neural networks necessarily perform badly if you use an asymmetric loss function.
There are many possible reasons why a neural network might perform badly.  If you wanted to test whether your loss is responsible for the problem, you could replace your asymmetric loss with a symmetric loss that is approximately equal for the regime of interest.  For instance, the Taylor series approximation of the function $f(x) = b(e^{ax} + ax - 1)$ is $f(x) = -b + 2abx + \frac12 a^2 b x^2 + O(x^3)$, so you could try training your network using the symmetric loss function $g(y,\hat{y}) = -b + \frac12 a^2 b (y-\hat{y})^2$ and see how well it works.  I conjecture it will behave about the same, but that's something you could test empirically.
It is unusual to min-max normalize outputs of the network.  I'm not even sure what that would involve.  Also if you are using the sigmoid activation function, then your outputs should already be normalized to be within -1..1, so it is not clear why you are normalizing them.
It is known that sigmoid and tanh activation functions often don't work that well; training can be very slow, or you can have problems with dead neurons.  Modern networks usually use a different activation function, e.g., ReLu.
There are many details to make a neural network train effectively, based on initialization, the optimization algorithm, learning rates, network architecture, and more.  I don't think you have any justification for concluding that the poor performance you are observing necessarily has anything to do with the asymmetry in your loss function.  And a question here might not be the best way to debug your network (certainly, the information provided here isn't enough to do so, and such a question is unlikely to be of interest to others in the future).
A: There are some examples for research papers using asymmetric cost functions / loss functions. One example is "Residual value forecasting using asymmetric cost functions" published in the International Journal for Forecasting. Various estimation methods considering asymmetric costs were used and compared - including neural networks.
https://www.sciencedirect.com/science/article/abs/pii/S0169207018300335
