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now essentially through this whole thing what we are doing is what is called as gradient
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descent learning so in this gradient descent learning what happens is that you have your
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w and and if you look over this is what is the gradient over there now as you see this
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the direction of this gradient which goes down now in that what essentially happens
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what happens in the weight space itself so if i plot down to different plots over here
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say that i have a very simple neuron we just associate two features to one single output
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with some random initial value over there and with this random initial value so we will
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have a point on the weight space as well as in this space of epochs versus my cost now
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based on my update rule over there on the gradient descent now with that i will get
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down a different value of cost coming down over here accordingly i get down to my next
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is the major fallacy which comes down and as we go down deeper and deeper we will come
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is that maybe you are at some value of w which is not exactly the minima so in case you are
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that implementation you will be able to relate down the ways of connecting these input images
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via certain features to or class of outputs now finally if you want to read more in details
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you are also welcome to use down matlab with the neural network toolbox which is has a
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much better gui and given the fact that a lot of people are most experienced on matlab
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you might be able to use it much faster but we would be sticking down to our options of
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doing it on python the other implementations are obviously based on lua torch which also
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so its a syntax and and the base library of torch which is one of the fastest ones as
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of date integrated within python to work it out ah so thats all i have for this particular
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so welcome to todays lecture and as from we will continue with what we have done on the
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last class so today is a practical lab based session in which we would be doing coding
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exercise so if you have followed down the last four lectures which we have finished
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off so the earlier lecture was on actually getting you introduced to a very linear perceptron
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which was basically a coding exercise and there we had implemented one particular code
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set as well as on the test set of c p od minus and then that was also stored down as a pickle
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file which is your local file used within python in order to store down your recorded
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matrices now today what we are going to do is build
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up on top of that so in the last class and i had concluded on the point where all of
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onwards where you have all the files which are saved down and then appropriately from
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those i am going to take it forward and create a new perceptron model and use these features
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which were already stored in a pickle file by loading it from the pickle file and subsequently
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go down to run a classification so the location is still the same so you will
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have to get it down from the github link where we have been keeping all our codes posted
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but the reason we preserved it if you would like to have all the earlier computation also
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and once you have calculated out the features you would go into it then this header actually
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needed as well as you will no more be requiring direct access to the torch vision data set
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because all the required information have been stored down in your pickle file itself
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so these are optionals but always a good guide to keep them keep going on
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now in the last class what we had done was we had trained them and we had stored them
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with your features from the training data there is another pickle file which stores
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such if i am not giving down a very explicit location this means that all these files reside
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some other location then you can just append down the extra directory location from where
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load this one so this is where you just define a file pointer as f and then you use that
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file pointer in order to load your pickle and you get your ah basically your arrays
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,nd to just display whether your matrices have been fetched out so lets keep on running
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one by one so this is the first model which has to be executed so once thats done so it
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works out you get your first instance which has been executed over there
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now we go from the comment on to the next one which is about loading so it shows that
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go down to the next one which is to define my network architecture ok so within my network
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architecture how it goes down is if you remember from our simple neural network so what we
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a ten class classification so it means that there are ten neurons on which the output
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will be coming down and these are a one hot neuron kind of a thing so what that technically
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is going to have a zero value over there ideally thats what is present on my training data
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set whenever you are predicting you will get one of the neurons which will have a very
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high value which is close to one all the other neurons are going to have a value which is
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there so the first part is to define an initialization part so first we will start by defining a
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class so this class definition is basically trying to define your container within python
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of saying that this is a particular one which i am using so what i am going to do is that
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we are going to import down my n n library so within n n i have a particular data type
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this initialization is trying to say down that what is the number of inputs which goes
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down into my neural network over here that is the on the input side of it and that
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is equal to my number of channels which i call over here as an underscore channels so
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this is exactly if you look over here so this n underscore channels it is supposed to be
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sort of like within the perceptron model over here which is the starting point of my pointer
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on the constructor and which is my end point of the constructor ok so the starting point
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of the constructor is what gets defined by this ,nd of super or which is just a superior
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constructor over there so over here the first part is that i will
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be defining my perceptron which has this and then my next part over there is that the perceptron
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the neurons which i have on my output side and how this is connected is that i have n
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number of channels in my input set which equals to the length of the feature vector and they
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connect down to all the ten neurons on my output side over there
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now typically for this initial part there wont be much of a modification subsequently
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one output vector so this is what initializes and defines my perceptron model
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the next part is that i need to define what is my forward pass over this model or forward
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pass means that if i am giving an input i get an output so what is the relationship
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between this input to my output ok now you remember from our perceptron model over there
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over there had to be connected down everything to my output and once i have this feed forward
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going down the next part is that there will be a summation which happens over there
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here so what this means over here is that whatever comes down as my input that gets
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it as input to this network and then i apply a soft max criteria over there
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called as perceptron whatever i give as input it will have a linear transformation then
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so this is how i define my perceptron model so lets run that part so i have my function
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like to do is actually generate a data set labels are accordingly so here if you remember
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so i was telling that in this classification problem you just have a one hot vector remaining
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everything else is going to be zero but then in the labels which we had stored so they
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had just numbers from one two three four five six seven eight nine ten so its its not exactly
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down another simple for loop so what it would do is that it would define
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elements in your training sample and ten is the number of output ah classes which can
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be present over there and now based on whichever is the class indicated in your train label
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over there so this part if that matches down to a particular column index on a given row
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then you are just going to set that as one and everything else is otherwise going to
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remain as zero based on this initialization given down over there so we can just run that
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part and this generates your one hot label vectors now once that is done
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the next part is that ah you can actually create a pytorch data set from your feature
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matrix and know where this comes down from the fact is that your earlier data structures
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and whatever videos you are using so they were all in numpy format and numpy is a library
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you are dealing with torch as another library it has its own data type definitions to go
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the functions which are needed are something which is called as a torch from numpy so what
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this effectively does is that given any array in numpy you are going to convert it into
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