Artificial Neural Networks ppt.pptx for final sem cse

www.studymafia.org
Submitted To: Submitted By:
www.studymafia.org www.studymafia.org
Seminar
On
Artificial Neural Networks

 INTRODUCTION
 HISTORY
 BIOLOGICAL NEURON MODEL
 ARTIFICIAL NEURON MODEL
 ARTIFICIAL NEURAL NETWORK
 NEURAL NETWORK ARCHITECTURE
 LEARNING
 BACKPROPAGATION ALGORITHM
 APPLICATIONS
 ADVANTAGES
 CONCLUSION

 “Neural“ is an adjective for neuron, and “network” denotes a
graph like structure.
 Artificial Neural Networks are also referred to as “neural
nets” , “artificial neural systems”, “parallel distributed
processing systems”, “connectionist systems”.
 For a computing systems to be called by these pretty names, it
is necessary for the system to have a labeled directed graph
structure where nodes performs some simple computations.
 “Directed Graph” consists of set of “nodes”(vertices) and a set
of “connections”(edges/links/arcs) connecting pair of nodes.
 A graph is said to be “labeled graph” if each connection is
associated with a label to identify some property of the
connection

Fig 1: AND gate graph
This graph cannot be considered a neural
network since the connections between the
nodes are fixed and appear to play no other
role than carrying the inputs to the node
that computed their conjunction.
Fig 2: AND gate network
The graph structure which connects the
weights modifiable using a learning
algorithm, qualifies the computing
system to be called an artificial neural
networks.
x2ϵ{0,1}
x1 x2
x1ϵ{0,1}
o = x1 AND x2
multiplier
(x1 w1)
(x2w2)
o = x1 AND x2
x1
x2
w1
w2
• The field of neural network was pioneered by BERNARD WIDROW of Stanford
University in 1950’s.
CONTD…

 late-1800's - Neural Networks appear as an analogy to biological
systems
 1960's and 70's – Simple neural networks appear
 Fall out of favor because the perceptron is not effective by itself, and
there were no good algorithms for multilayer nets
 1986 – Backpropagation algorithm appears
 Neural Networks have a resurgence in popularity

 Records (examples) need to be represented as a (possibly large)
set of tuples of <attribute, value>
 The output values can be represented as a discrete value, a real
value, or a vector of values
 Tolerant to noise in input data
 Time factor
 It takes long time for training
 Once trained, an ANN produces output values (predictions) fast
 It is hard for human to interpret the process of prediction by
ANN

Four parts of a typical nerve cell : -
 DENDRITES: Accepts the inputs
 SOMA : Process the inputs
 AXON : Turns the processed
inputs into outputs.
 SYNAPSES : The electrochemical
contact between
the neurons.

 Inputs to the network are
represented by the mathematical
symbol, xn
 Each of these inputs are multiplied
by a connection weight , wn
sum = w1 x1 + ……+ wnxn
 These products are simply summed,
fed through the transfer function, f(
) to generate a result and then
output.
f
w1
w2
xn
x2
x1
wn
f(w1 x1 + ……+ wnxn)

Biological Terminology Artificial Neural Network Terminology
Neuron Node/Unit/Cell/Neurode
Synapse Connection/Edge/Link
Synaptic Efficiency Connection Strength/Weight
Firing frequency Node output

 Artificial Neural Network (ANNs) are programs
designed to solve any problem by trying to mimic the
structure and the function of our nervous system.
 Neural networks are based on simulated neurons,
Which are joined together in a variety of ways to form
networks.
 Neural network resembles the human brain in the
following two ways: -
* A neural network acquires knowledge through
learning.
*A neural network’s knowledge is stored within the
interconnection strengths known as synaptic
weight.

output layer
connections
Input layer
Hidden layers
Neural network
Including
connections
(called weights)
between neuron
Comp
are
Actual
output
Desired
output
Input
output
Figure showing adjust of neural
network
Fig 1 : artificial neural network model
CONTD…

The neural network in which every node
is connected to every other nodes, and
these connections may be either
excitatory (positive weights), inhibitory
(negative weights), or irrelevant (almost
zero weights).
These are networks in which nodes
are partitioned into subsets called
layers, with no connections from
layer j to k if j > k.
Input node
Input node
output node
output node
Hidden node
Layer 1 Layer2
Layer0 Layer3
(Input layer) (Output layer)
Hidden Layer
Fig: fully connected
network
fig: layered network

This is the subclass of the layered
networks in which there is no intra-
layer connections. In other words, a
connection may exist between any
node in layer i and any node in layer j
for i < j, but a connection is not allowed
for i=j.
fig : Feedforward network
This is a subclass of acyclic
networks in which a connection
is allowed from a node in layer i
only to nodes in layer i+1
Layer 1 Layer2
Layer0 Layer3
Hidden Layer
Layer 1 Layer2
Layer0 Layer3
Hidden Layer
Fig : Acyclic network
CONTD…

Many problems are best solved using
neural networks whose architecture
consists of several modules, with sparse
interconnections between them. Modules
can be organized in several different ways
as Hierarchial organization, Successive
refinement, Input modularity
Fig : Modular neural network
CONTD…

 Neurons in an animal’s brain are “hard wired”. It is
equally obvious that animals, especially higher order
animals, learn as they grow.
 How does this learning occur?
 What are possible mathematical models of learning?
 In artificial neural networks, learning refers to the method
of modifying the weights of connections between the
nodes of a specified network.
 The learning ability of a neural network is determined by
its architecture and by the algorithmic method chosen for
training.

UNSUPERVISED
LEARNING
 This is learning by doing.
 In this approach no sample
outputs are provided to the
network against which it can
measure its predictive
performance for a given
vector of inputs.
 One common form of
unsupervised learning is
clustering where we try to
categorize data in different
clusters by their similarity.
• A teacher is available to indicate
whether a system is performing
correctly, or to indicate the amount of
error in system performance. Here a
teacher is a set of training data.
• The training data consist of pairs of
input and desired output values that
are traditionally represented in data
vectors.
• Supervised learning can also be
referred as classification, where we
have a wide range of classifiers,
(Multilayer perceptron, k nearest
neighbor..etc)
SUPERVISED LEARNING
CONTD…

 The backpropagation algorithm (Rumelhart and McClelland,
1986) is used in layered feed-forward Artificial Neural
Networks.
 Back propagation is a multi-layer feed forward, supervised
learning network based on gradient descent learning rule.
 we provide the algorithm with examples of the inputs and
outputs we want the network to compute, and then the error
(difference between actual and expected results) is calculated.
 The idea of the backpropagation algorithm is to reduce this
error, until the Artificial Neural Network learns the training
data.

 The activation function of the artificial neurons in
ANNs implementing the backpropagation
algorithm is a weighted sum (the sum of the inputs
xi multiplied by their respective weights wji)
 The most common output function is the sigmoidal
function:
 Since the error is the difference between the actual
and the desired output, the error depends on the
weights, and we need to adjust the weights in
order to minimize the error. We can define the
error function for the output of each neuron:
Inputs, x
Weights, v weights, w
output
Fig: Basic Block of
Back propagation neural network

 The backpropagation algorithm now calculates how the error depends on the
output, inputs, and weights.
the adjustment of each weight (Δwji ) will be the negative of a constant eta (η)
multiplied by the dependance of the “wji” previous weight on the error of the
network.
 First, we need to calculate how much the error depends on the output
 Next, how much the output depends on the activation, which in turn depends
on the weights
 And so, the adjustment to each weight will be
CONTD…

 If we want to adjust vik, the weights (let’s call them vik ) of a
previous
layer, we need first to calculate how the error depends not on
the
weight, but in the input from the previous layer i.e. replacing
w by x
as shown in below equation.
where
 and
Inputs, x
Weights, v weights, w
output
CONTD…

 Neural Networks in Practice
 Neural networks in medicine
• Modelling and Diagnosing the Cardiovascular System
• Electronic noses
• Instant Physician
 Neural Networks in business
 Marketing
 Credit Evaluation

 It involves human like thinking.
 They handle noisy or missing data.
 They can work with large number of variables or
parameters.
 They provide general solutions with good predictive
accuracy.
 System has got property of continuous learning.
 They deal with the non-linearity in the world in
which we live.

• Artificial neural networks are inspired by the learning processes that
take place in biological systems.
• Artificial neurons and neural networks try to imitate the working
mechanisms of their biological counterparts.
• Learning can be perceived as an optimisation process.
• Biological neural learning happens by the modification of the
synaptic strength. Artificial neural networks learn in the same way.
• The synapse strength modification rules for artificial neural networks
can be derived by applying mathematical optimisation methods.

• Learning tasks of artificial neural networks can be reformulated as
function approximation tasks.
• Neural networks can be considered as nonlinear function
approximating tools (i.e., linear combinations of nonlinear basis
functions), where the parameters of the networks should be found by
applying optimisation methods.
• The optimisation is done with respect to the approximation error
measure.
• In general it is enough to have a single hidden layer neural network
(MLP, RBF or other) to learn the approximation of a nonlinear
function. In such cases general optimisation can be applied to find the
change rules for the synaptic weights.

 www.google.com
 www.wikipedia.com
 www.studymafia.org

Artificial Neural Networks ppt.pptx for final sem cse

More Related Content

Similar to Artificial Neural Networks ppt.pptx for final sem cse

Recently uploaded

Artificial Neural Networks ppt.pptx for final sem cse