What's the correct reasoning behind solving the vanishing/exploding gradient problem in deep neural...












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I have read several blog posts where the solution to solve the vanishing/exploding gradient problem in a deep neural network is suggested to be using Relu activation function instead of tanH & sigmoid.



But, I have encountered an explanation by Prof. Andrew NG lecture that explains that a partial solution to the vanishing gradient problem is a better or more careful choice of the random initialization of weights in your neural network.



i.e the solution is:



To set the variance of Wi to be equal to 1/n, where n is the number of input features that are going into a neuron. Along with the assumption that the input features of activations are roughly mean 0 and standard variance 1. So, what it's doing is that it's trying to set each of the weight matrices w so that it's not too much bigger than 1 and not too much less than 1, therefore, it doesn't explode or vanish too quickly.




  • So, if you are using a ReLu activation function then setting the variance of Wi to be equal to sqrt(2/n) works better**.

  • and if you are using a TanH activation function then setting the variance of Wi to be equal to sqrt(2/n) works better.

  • or in some cases, it's being suggested to use Xavier initialization

  • Also, if we need we can tune of variance parameter as another hyperparameter by multiplying into the above formula and tune that multiplier as part of your hyperparameter search.


Therefore, choosing a reasonable scaling for how to initialize the weights helps weights not to explode too quickly and not decay to zero too quickly, which in turn could help in training a reasonably deep network without the weights or the gradients exploding or vanishing too much and not simply using ReLu!.
Please correct me if my understanding is wrong or incomplete!










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    1












    $begingroup$


    I have read several blog posts where the solution to solve the vanishing/exploding gradient problem in a deep neural network is suggested to be using Relu activation function instead of tanH & sigmoid.



    But, I have encountered an explanation by Prof. Andrew NG lecture that explains that a partial solution to the vanishing gradient problem is a better or more careful choice of the random initialization of weights in your neural network.



    i.e the solution is:



    To set the variance of Wi to be equal to 1/n, where n is the number of input features that are going into a neuron. Along with the assumption that the input features of activations are roughly mean 0 and standard variance 1. So, what it's doing is that it's trying to set each of the weight matrices w so that it's not too much bigger than 1 and not too much less than 1, therefore, it doesn't explode or vanish too quickly.




    • So, if you are using a ReLu activation function then setting the variance of Wi to be equal to sqrt(2/n) works better**.

    • and if you are using a TanH activation function then setting the variance of Wi to be equal to sqrt(2/n) works better.

    • or in some cases, it's being suggested to use Xavier initialization

    • Also, if we need we can tune of variance parameter as another hyperparameter by multiplying into the above formula and tune that multiplier as part of your hyperparameter search.


    Therefore, choosing a reasonable scaling for how to initialize the weights helps weights not to explode too quickly and not decay to zero too quickly, which in turn could help in training a reasonably deep network without the weights or the gradients exploding or vanishing too much and not simply using ReLu!.
    Please correct me if my understanding is wrong or incomplete!










    share|improve this question









    $endgroup$















      1












      1








      1





      $begingroup$


      I have read several blog posts where the solution to solve the vanishing/exploding gradient problem in a deep neural network is suggested to be using Relu activation function instead of tanH & sigmoid.



      But, I have encountered an explanation by Prof. Andrew NG lecture that explains that a partial solution to the vanishing gradient problem is a better or more careful choice of the random initialization of weights in your neural network.



      i.e the solution is:



      To set the variance of Wi to be equal to 1/n, where n is the number of input features that are going into a neuron. Along with the assumption that the input features of activations are roughly mean 0 and standard variance 1. So, what it's doing is that it's trying to set each of the weight matrices w so that it's not too much bigger than 1 and not too much less than 1, therefore, it doesn't explode or vanish too quickly.




      • So, if you are using a ReLu activation function then setting the variance of Wi to be equal to sqrt(2/n) works better**.

      • and if you are using a TanH activation function then setting the variance of Wi to be equal to sqrt(2/n) works better.

      • or in some cases, it's being suggested to use Xavier initialization

      • Also, if we need we can tune of variance parameter as another hyperparameter by multiplying into the above formula and tune that multiplier as part of your hyperparameter search.


      Therefore, choosing a reasonable scaling for how to initialize the weights helps weights not to explode too quickly and not decay to zero too quickly, which in turn could help in training a reasonably deep network without the weights or the gradients exploding or vanishing too much and not simply using ReLu!.
      Please correct me if my understanding is wrong or incomplete!










      share|improve this question









      $endgroup$




      I have read several blog posts where the solution to solve the vanishing/exploding gradient problem in a deep neural network is suggested to be using Relu activation function instead of tanH & sigmoid.



      But, I have encountered an explanation by Prof. Andrew NG lecture that explains that a partial solution to the vanishing gradient problem is a better or more careful choice of the random initialization of weights in your neural network.



      i.e the solution is:



      To set the variance of Wi to be equal to 1/n, where n is the number of input features that are going into a neuron. Along with the assumption that the input features of activations are roughly mean 0 and standard variance 1. So, what it's doing is that it's trying to set each of the weight matrices w so that it's not too much bigger than 1 and not too much less than 1, therefore, it doesn't explode or vanish too quickly.




      • So, if you are using a ReLu activation function then setting the variance of Wi to be equal to sqrt(2/n) works better**.

      • and if you are using a TanH activation function then setting the variance of Wi to be equal to sqrt(2/n) works better.

      • or in some cases, it's being suggested to use Xavier initialization

      • Also, if we need we can tune of variance parameter as another hyperparameter by multiplying into the above formula and tune that multiplier as part of your hyperparameter search.


      Therefore, choosing a reasonable scaling for how to initialize the weights helps weights not to explode too quickly and not decay to zero too quickly, which in turn could help in training a reasonably deep network without the weights or the gradients exploding or vanishing too much and not simply using ReLu!.
      Please correct me if my understanding is wrong or incomplete!







      deep-learning activation-function






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