Archives / 2015 / November
  • Simple math behind neuron

    Hello everybody,

    today I want to share with you some ideas about activation functions in neural networks. 

    But before I'll do this let's see simplified edition of neuron:

    As usually many books describe following schema of working neuron:

    ignals go into dendrites into neuron body. Neuron body does some kind of converting signal into another signal and sends output through axon to another neuron.

    What is origin of signals, or where they come from? It can be any place of your body. It can be your eyes, it can be your nose, it can be touching of your hand, etc. Anything 

    that your body signals is processed in the brain. 

    So now, imagine, that you are mathematician and want to provide … more

  • Hierarchical storage of data in databases

    Hello everybody,

    today I want to write about hierarchical storage of information in databases.

    As usually for storing hierarchy you'll have a choice: fast reading or fast writing. Fast reading as usually related with nested sets, and fast writing is related with adjacency. Also you can consider some kind of combination of both methods.

    Following urls give good generalization of what you can have as good generalization

    One more Nested Intervals vs. Adjacency List comparison: really cool comparison

    Models for hierarchical data with SQL and PHP: Bill Karwin gives good comparison as well in slides

    Representing hierarchies in MySQL: nice watching of Nested Set … more

  • Jenkins and CI

    Hello everybody,

    few days ago I had chance of configuring Jenkins. 

    I will ommit purpose and value of CI, just want to mention one error message, which you can find if install MSBuild plugin for building .sln file.

    If you point to MSBuild file, I mean msbuild.exe file, you'll see interesting warning message:

    d:\msbuildsln.bat is not a directory on the Jenkins master (but perhaps it exists on some slaves)

    For  me purpose and value of this message is puzzle till know, but just want to write that you can ignore this message without any side-effects more

  • Spies and secret agents in javascript

    Hello everybody,

    Have you ever had a desire to become chief of secreat agent or spy? To be honest I never had such desire, but unwilignly I become chief of spies  and secret agents which I created in javascript. 

    To put simply during unit testing of javascript sometime is needed to mock calling to some functions with replacement of that function, and sometime there is a need to mock that function without it's replacement. 

    The first scenario is much easier to implement, while the second one required usage of apply function. 

    Take a look at the following picture:

    There are many js libraries which support both options ( with and without original function ). For example jasmine, … more

  • AngularJS ng-options

    Hello everybody,

    today I want to make some post about how to work with AngularJS select directive from viewpoint of complicated objects. 

    <select id="type"

                  class="form-control" name="type" aria-readonly="true"


                     <option ng-selected="{{ course.courseId== }}"

                       ng-repeat="et in courseTypes" value="{{}}">{{}}



    In controller I have some code which populates data from controller for course types, and in order to display complicated parts I applied mentioned before select. more