# Build a Neural Net in 4 Minutes

Hello world, welcome to Sirajology. Today, we’re going to be building

a neural net in four minutes, let’s get started. There are like a million and one

machine learning models out there, but neural nets in particular have gotten

really popular recently because of two things,

faster computers and more data. They’ve helped produce some amazing

breakthroughs in everything from image recognition to

generating rap songs. There’s really just 3 steps

involved in machine learning. Build it. Train it. and test it. Once we build our model we can

train it against our input and output data to make it better and

better at pattern recognition. So, let’s build our model. A three layer neural network in Python. We’ll want to start off by importing

NumPy, which is my go to library for scientific computing in Python. Then, we’ll want to create

a function that will map any value to a value between zero and one. This is called a sigmoid. This function will be run in every

neuron of our network when data hits it. It’s useful for

creating probabilities out of numbers. Once we’ve created that, let’s initialize our input

data set as a matrix. Each row is a different

training example. Each column represents

a different neuron. So we have four training examples

with three input neurons each. Then we’ll create our output data set. Four examples, one output neuron each. Since we’ll be generating

random numbers in a second, let’s seed them to make

them deterministic. This just means give random numbers that

are generated the same starting point or seed so that we’ll get the same

sequence of generated numbers every time we run our program. This is useful for debugging. Next, we’ll create our synapse matrices. Synapses are the connections

between each neuron in one layer to every neuron in the next layer. Since we will have three layers in our

network, we need two synapses matrixes. Each synapse has a random

weight assigned to it. After that,

we’ll begin the training code. We’ll create a for-loop that

iterates over the training code to optimize the network for

the given data set. We’ll start of by

creating our first layer. It’s just our input data. Now comes the prediction step. We’ll perform matrix multiplication

between each layer and its synapse. Then we’ll run our sigmoid function on

all the values in the matrix to create the next layer. The next layer contains

a prediction of the output data. Then we do the same thing on that

layer to get our next layer, which is a more refined prediction. So now that we have a prediction of the

output value in layer two, let’s compare it to the expected output data using

subtraction to get the error rate. We’ll also want to print out the average

error rate at a set interval to make sure it goes down every time. Next, we’ll multiply our error rate by

the result of our sigmoid function. The function is used to get the

derivative of our output prediction from layer two. This will give us a delta which we’ll

use to reduce the error rate of our predictions when we update

our synapses every iteration. Then we’ll want to see how much layer

one contributed to the error in layer two. This is called back propagation. We’ll get this error by

multiplying layer two’s delta by synapse one’s transpose. Then we’ll get layer one’s

delta by multiplying its error by the result of

our sigmoid function. The function is used to get

the derivative of layer one. Now that we have deltas for each of

our layers, we can use them to update our synapse rates to reduce the error

rate more and more every iteration. This is an algorithm

called gradient descent. To do this, we’ll just multiply

each layer by a delta. Finally, let’s print

the predicted output. And there you have it. Let’s run this in Terminal and

see what we get. Awesome, we can see that our error

rate decreases every iteration and the predicted output is very,

very close to the actual output. There is so much we can do to

improve our neural network. For more information check out

the links in the description below and please subscribe for

more technology videos. Thanks for watching.

Wow, wonderful, now you are appointed as the Next Director of NASA in the 5th Minute…

Congratulations…

That moment that you didn't code with Python in years and you updated from 2.7 to 3.7 and you're stuck in a print function (

FOR AN HOUR)Finally a real reason for me to be taking pre calc right now

Super cool. I don't have any programming experiencie but still I found this really interesting. Suscribed

What is this syntax you used in "deriv-False" in python function: def nonlin(x, deriv-False)

it takes deriv argument and if its not passed default is False?

With R would be better.

thats to fast

Sir I don’t know what the fuck you just said or why I watched the whole video. But good job

Uh, I know it's an old video of yours Siraj, but don't you think it's a bit complex for beginners?

Complex Neural Networks now under 5 minutes with Tensorflow/Keras/PyTorch. But it's still a pain in the ass to prepare the data to fit the model ahahha

Bought my neural net for $20 which took only a click of the mouse!

Hey Siraj…plz call me …i won2discuss abt a project called neural science…for UAE…

Hey Siraj…plz call me …i won2discuss abt a project called neural science…for UAE…

Anyone make a video on how to understand this video

Hi guys, can somebody help. I have this error NameError: name 'xrange' is not defined

Can you please make a 1 day video on this?

the moment you know that it was a click bait because he taught that in just 3:26 minutes

what program did you use, I assume its python but it doesn't look the same as mine.

wait how do I get the pyton version like yours mine looks like the one that you get when downloading windows and the one they use in the matrix with the green letters and black background I forgot what it's called?

Can anybody tell me which Python environment this is, please?

That was speedy

Not helpful

*HELP AS FAST AS U CAN PLS ;(((*SyntaxError: invalid syntax

PS C:UsersJan ZienkiewiczDesktopKasztaneqBOT Xkkk> py ai.py

File "ai.py", line 11

[1,1,1]])

^

SyntaxError: invalid syntax

I couldn't spare 2 minutes so I watched it at 4x. Problem was that Siraj sounds like Alvin the Chipmunk at 4x

You lost me at "Let's get started"

Love that video, went right to the point.

I think you should do 40mins video of the same thing exactly – but this time SLOWER…. MUCH MUCH SLOWER….And with more details. Only THEN it'll be a good video. As speed is not the target here – but understanding.

I don't really understand anything… But one day I will

Something similar in javascript???? How to keep the experience that neural network has got, so next time you run it it remembers all the previous training and can continue to train more for a better result?

would relu work better as an activation fn?

With the 3 typos corrected (as discussed in the coms below), this exact code in the video works great! Thanks, Siraj!

Why do you over-react so much?

OK that was not help full at all. I'm not dum or anything but please, make sense.

Ok this showed up in my recommendation! I found the crazy Siraj!

How can we create multiple layers to create a brain?

Still indian faced and indian mentality, trying to pass amongst europoid skulls.

Aaaaaaand I have no idea what you said.

Hi Siraj,

I appreciate your effort to educate people.

Looks like your verbal delivered code and github codes are different. Please upload the same code or email to me.

Thanks

garbage…

Can u suggest some of deep learning project topics?

What's the purpose ?

Thank you so much Siraj!! You are the man!

Instructions not clear, created doomsday robot that wants to kill everyone

Hi Siraj, Please Which neural network algorithm is best applied on malware classification? Thanks Siraj

X = np.array([0,0,1]) instead of X = np.array([0.0,1])

1+1=2 ok got it.

Amazing video !!! please tell me why have you multiplied the synapse matrix by 2 and subtracted 1 in line 24 and 25 ?

I just came here to say that I totally understood everything he just said 🙂

4mins but video is 3:27…..

Clickbait: Am I a joke to you?

How much speed did you take? 😂

Hello man

Your videos are more confusing then informative.

Anyways thanks for a litttttttttle information your videos give

What

numpy doesn't work

Yeah I understood everything

This isn't teaching, it's taking the piss.

this is a slap in the face for everyone who didnt program before

This is the single best video on youtube I've watched so far. Efficiency wise.

Anyone know of a good place to learn the context of this code? I know, I know, I'm here on the lazy person's tutorial. But longer videos I've watched seem to still expect me to know more. Anyone know of a good series to follow for absolute beginners?

This video is faked …..The code doesn't work and he ran a different file than what he typed.

I prefer

import numpy as numericpython

Thank you for posting the suggested articles in your description. Those are helping out soooo much for understanding neural networks!!!!

how to test???

Can you give me full neural network script in word format

I subscribed and I am wondering why everyone is in a hurry. Nobody can slow down any more.

OK , you show training. But now how to use it ? how to send input and prediction ?

No one:

Siraj: import numpy as numpy

This video demotivates me trying to learn python. I will never understand this

cringy channel

OK i don't have a computer. 😢

dope

Whats the purpose in doing it in 4 minutes anyway????

can someome direct me to a really good video on HOW TO MAKE A LEARNING AI i wanna make some experiments too

The speed is fine to me. I mean you can pause the video anytime…

why is my error rate constantly not depleting and keeping the same rate

…whAT?!?!

This helped alot, thank you!

terrible teacher

Which software u use to create videos and graphics in your videos?

What program is that

Awesome! Can you do long& thorough podcasts with engineers working in AI& ML& Data Analysis fields ? 😀

Anyone get any of that?

He imported numpy as numpy and then used np 😂

can someone explain what exactly happened with those numbers? is this some logic gate simulation? like 0,0,1 —> 0 and 1,0,1 –>1?

Are you professional data analysis scientist ?

Clear, concise, eloquent. I think Siraj is actually an AI bot who has been brought back from the future to help save humanity. Or to hasten our conquest by our robot overlord masters. Not sure yet, but I'm on board.

I understand all of it, except why we need a hidden layer. Why can't we just do a single layer perceptron for this?

import numpy as np

def sigmoid(x):

return 1 / (1 + np.exp(-x))

def sigmoid_derivative(x):

return x * (1 – x)

training_inputs = np.array([[0,0,1],

[1,1,1],

[1,0,1],

[0,1,1]])

training_outputs = np.array([[0,1,1,0]]).T

np.random.seed(1)

synaptic_weights = 2 * np.random.random((3, 1)) -1

for iteration in range(10):

print('random starting synaptic weights: ')

print(synaptic_weights)

input_layer = training_inputs

stuff = np.dot(input_layer, synaptic_weights)

outputs = sigmoid(np.dot(input_layer, synaptic_weights))

error = training_outputs – outputs

adjustments = error * sigmoid_derivative(outputs)

synaptic_weights += np.dot(input_layer.T, adjustments)

print("synaptic weights after training")

print(synaptic_weights)

print('outputs after training: ')

print(outputs)

What? I didn’t understand a single thing lol

I watched this video, and built an AI what colonized mars in 4 minutes!

i was about to search "how to make a neural network in python"

when you said LET'S USE PYTHON

how do i go from this to ai that beat games or write songs?

Iv'e seen the same example so many times and dont know how to actually apply this to a real world example. someone help please

book for deep learning and neural networks from zero updated?

I did this in MATLAB because I don't know python. Glad it worked.

This video name shold be: "I don't understand what I am doing and my onscreen code consists of mistakes". Guys, don't waste your precious 4 minutes of yor life.

I honestly believe people who make 4 minute videos on huge topics like neural networks and especially "showing" them how to code it is such a bad way to learn. You want to learn how to build a NN? Can't be done in 4 minutes. You can read an article for 4 minutes on Neural Networks and learn so much more with actual understanding rather than this dude pretending like he actually knows what he is talking about.

um, so, what i got was, You need to propagate the perpendicular bisectors, that way the circumference eliminates the overall variable decay.

or something like that

slimy……. Yet satisfyingWell may I add, the code in the background is complete dogshit, and aside from the fact, that he very obviously copied some of that code from somewhere else, there are so many syntax errors in this code that i'm just disappointed. I mean I'm not the greatest programmer in the world, but dude. You literally used dots instead of commas in line 12, closed a bracket too much immedeately after, imported numpy as numpy but used np everywhere, then wrote a comma instead of a dot in line 8, which makes it look like you're adding the module numpy to one, in a tuple, which then divides 1 and returns the result. I'm not sure, but it looks like you wrote a – instead of a = in line 3, and I can't tell, because the video resolution is so bad.

But aside from that, your code works. The guy who actually wrote it deserves respect.

Can this code be used with the latest version of python

How to install numpy, i am having some difficulty (i don't know how to get numpy)