Introduction¶

This introductory page is a big long, but that's because all the below concepts are common to every upcoming topic.

Machine Learning¶

Field of study that enables computers to learn without being explicitly programmed; machine learns how to perform task \(T\) from experience \(E\) with performance measure \(P\).

Machine learning is necessary when it is not possible for us to make rules, ie, easier for the machine to learn the rules on its own

flowchart LR

subgraph Machine Learning
    direction LR
    i2[Past<br/>Input] & o2[Past<br/>Output] -->
    a(( )) -->
    r2[Derived<br/>Rules/<br/>Functions]

    r2 & ni[New<br/>Input] -->
    c(( )) -->
    no[New<br/>Output]
end

subgraph Traditional Programming
    direction LR
    r1[Standard<br/>Rules/<br/>Functions] & i1[New<br/>Input] -->
    b(( )) -->
    o1[New<br/>Output]
end

Why do we need ML?¶

To perform tasks which are easy for humans, but difficult to generate a computer program for it

Requirements¶

\(\exists\) pattern
If \(\not \exists\) pattern and its just noise, it is impossible to model it
We cannot quantify pattern mathematically
\(\exists\) data

Guiding Principles¶

Principle	Questions
Relevance	Is the use of ML in a given context solving an appropriate problem
Representativeness	Is the training data appropriately selected
Value	- Do the predictions inform human decisions in a meaningful way - Does the machine learning model produce more accurate predictions than alternative methods - Does it explain variation more completely than alternative methods
Explainability	- Data selection, Model selection, (un)intended consequences - How effectively is use of ML communicated
Auditability	Can the model's decision process be queried/monitored by external actors
Equity	The model should benefit/harm one group disproportionately
Accountability/Responsibility	Are there mechanisms in place to ensure that someone will be responsible for responding to feedback and redressing harms, if necessary?

Learning Problem¶

Given training examples and hypothesis set of candidate models, generate a hypothesis function using a learning algorithm to estimate an unknown target function

\(P(x)\) quantifies relative importance of \(x\)

Learning model

Learning algorithm
Hypothesis set

Stages of Machine Learning¶

flowchart LR
td[Task<br/>Definition] -->
cd[(Collecting<br/>Data)] -->
l[Learning<br/>Type] -->
c[Define Cost] -->
Optimize -->
Evaluate -->
Tune -->
save[/Save Model/] -->
d[/Deploy/] --> Model
cd --> ad
ld[(Live <br/>Data)] --> ad[Anomaly<br/>Detection] --> Model

3 Dimensions of Prediction¶

Point estimate
Time
Probabilistic
Intervals
Density
Trajectories/Scenarios

Good Prediction Characteristics¶

Forecast/Prediction consistency: Forecasts/Predictions should correspond to forecaster’s best judgement on future events, based on the knowledge available at the time of issuing the Forecasts/Predictions
Forecast/Prediction quality (accuracy): Forecasts/Predictions should describe future events as good as possible, regardless of what these Forecasts/Predictions may be used for
Forecast/Prediction value: Forecasts/Predictions should bring additional benefits (monetary/others) when used as input to decision-making

Hence, sometimes you may choose the Forecast/Prediction with the better value even if its quality is not the best

Performance vs Parsimony¶

Parsimonious models are more explainable
Parsimonious models generalize better
Small gains with deep models may disappear with dataset shift/non-stationary

Aspects¶

Aspect	Equivalent in Marco Polo game
Loss	Goal
Model Class	Map
Optimization	Search
Data	Sound

Open-source Tools¶


Scikit-Learn
TensorFLow
Keras
PyTorch
MXNet
CNTK
Caffe
PaddlePaddle
Weka

Doesn’t do well for Forecasting¶

Machine Learning cannot provide reliable time-series forecasting, without causal reasoning. This is why AI/ML cannot be blindly trusted for stock price prediction.