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15 Math Concepts Every Data Scientist Should Know

You're reading from   15 Math Concepts Every Data Scientist Should Know Understand and learn how to apply the math behind data science algorithms

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Product type Paperback
Published in Aug 2024
Publisher Packt
ISBN-13 9781837634187
Length 510 pages
Edition 1st Edition
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Author (1):
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David Hoyle David Hoyle
Author Profile Icon David Hoyle
David Hoyle
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Table of Contents (21) Chapters Close

Preface 1. Part 1: Essential Concepts FREE CHAPTER
2. Chapter 1: Recap of Mathematical Notation and Terminology 3. Chapter 2: Random Variables and Probability Distributions 4. Chapter 3: Matrices and Linear Algebra 5. Chapter 4: Loss Functions and Optimization 6. Chapter 5: Probabilistic Modeling 7. Part 2: Intermediate Concepts
8. Chapter 6: Time Series and Forecasting 9. Chapter 7: Hypothesis Testing 10. Chapter 8: Model Complexity 11. Chapter 9: Function Decomposition 12. Chapter 10: Network Analysis 13. Part 3: Selected Advanced Concepts
14. Chapter 11: Dynamical Systems 15. Chapter 12: Kernel Methods 16. Chapter 13: Information Theory 17. Chapter 14: Non-Parametric Bayesian Methods 18. Chapter 15: Random Matrices 19. Index 20. Other Books You May Enjoy

Exercises

Here is a series of exercises. The answers to all the exercises are given in the Answers_to_Exercises_Chap6.ipynb Jupyter notebook in the GitHub repository.

  1. For the AR(1) process defined by the following equation,

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block"><mrow><mrow><msub><mi>y</mi><mi>t</mi></msub><mo>=</mo><mi>ϕ</mi><msub><mi>y</mi><mrow><mi>t</mi><mo>−</mo><mn>1</mn></mrow></msub><mo>+</mo><msub><mi>ε</mi><mi>t</mi></msub><msub><mi>ε</mi><mi>t</mi></msub><mo>~</mo><mtext>Normal</mtext><mfenced open="(" close=")"><mrow><mn>0</mn><mo>,</mo><msup><mi>σ</mi><mn>2</mn></msup></mrow></mfenced></mrow></mrow></math>

Eq. 35

show that <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><mi mathvariant="double-struck">E</mi><mfenced open="(" close=")"><msub><mi>y</mi><mi>t</mi></msub></mfenced><mo>→</mo><mn>0</mn></mrow></mrow></math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math"><mml:mtext>Var</mml:mtext><mml:mfenced separators="|"><mml:mrow><mml:msub><mml:mrow><mml:mi>y</mml:mi></mml:mrow><mml:mrow><mml:mi>t</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mfenced><mml:mo>→</mml:mo><mml:msup><mml:mrow><mml:mi>σ</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup><mml:mo>/</mml:mo><mml:mfenced separators="|"><mml:mrow><mml:mn>1</mml:mn><mml:mo>-</mml:mo><mml:msup><mml:mrow><mml:mi>ϕ</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:mfenced></mml:math> as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math"><mml:mi>t</mml:mi><mml:mo>→</mml:mo><mml:mi>∞</mml:mi></mml:math>, for any starting value <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math"><mml:msub><mml:mrow><mml:mi>y</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msub></mml:math>. For this exercise you can assume that <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><mn>0</mn><mo><</mo><mi>ϕ</mi><mo><</mo><mn>1</mn></mrow></mrow></math>.

2. For the AR(1) process defined by the following equation,

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block"><mrow><mrow><msub><mi>y</mi><mi>t</mi></msub><mo>=</mo><mfenced open="(" close=")"><mrow><mn>1</mn><mo>−</mo><mi>ϕ</mi></mrow></mfenced><mi>μ</mi><mo>+</mo><mi>ϕ</mi><msub><mi>y</mi><mrow><mi>t</mi><mo>−</mo><mn>1</mn></mrow></msub><mo>+</mo><msub><mi>ε</mi><mi>t</mi></msub><msub><mi>ε</mi><mi>t</mi></msub><mo>~</mo><mtext>Normal</mtext><mfenced open="(" close=")"><mrow><mn>0</mn><mo>,</mo><msup><mi>σ</mi><mn>2</mn></msup></mrow></mfenced></mrow></mrow></math>

Eq. 36

show that <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><mi mathvariant="double-struck">E</mi><mfenced open="(" close=")"><msub><mi>y</mi><mi>t</mi></msub></mfenced><mo>→</mo><mi>μ</mi></mrow></mrow></math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math"><mml:mtext>Var</mml:mtext><mml:mfenced separators="|"><mml:mrow><mml:msub><mml:mrow><mml:mi>y</mml:mi></mml:mrow><mml:mrow><mml:mi>t</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mfenced><mml:mo>→</mml:mo><mml:msup><mml:mrow><mml:mi>σ</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup><mml:mo>/</mml:mo><mml:mfenced separators="|"><mml:mrow><mml:mn>1</mml:mn><mml:mo>-</mml:mo><mml:msup><mml:mrow><mml:mi>ϕ</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:mfenced></mml:math> as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math"><mml:mi>t</mml:mi><mml:mo>→</mml:mo><mml:mi>∞</mml:mi></mml:math>, for any starting value <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math"><mml:msub><mml:mrow><mml:mi>y</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msub></mml:math>. For this exercise, you can assume that <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><mn>0</mn><mo><</mo><mi>ϕ</mi><mo><</mo><mn>1</mn></mrow></mrow></math>. See if you can derive the values of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math"><mml:mi mathvariant="double-struck">E</mml:mi><mml:mfenced separators="|"><mml:mrow><mml:msub><mml:mrow><mml:mi>y</mml:mi></mml:mrow><mml:mrow><mml:mi>t</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mfenced></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math"><mml:mtext>Var</mml:mtext><mml:mfenced separators="|"><mml:mrow><mml:msub><mml:mrow><mml:mi>y</mml:mi></mml:mrow><mml:mrow><mml:mi>t</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mfenced></mml:math> for any value of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math"><mml:mi>t</mml:mi></mml:math>, not just the asymptotically limiting values.

3. Use the ARIMA model form in Eq. 28 to generate a sample time series of length <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math"><mml:mi>T</mml:mi><mml:mo>=</mml:mo><mml:mn>500</mml:mn></mml:math> timepoints, that is of order <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math"><mml:mi>p</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mi>d</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mi>q</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:math>, with coefficients <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><msub><mi>ϕ</mi><mn>1</mn></msub><mo>=</mo><mn>0.6</mn><mo>,</mo><msub><mi>θ</mi><mn>1</mn></msub><mo>=</mo><mn>0.7</mn></mrow></mrow></math>. The noise values should be i.i.d. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math"><mml:mtext>Normal</mml:mtext><mml:mfenced separators="|"><mml:mrow><mml:mn>0</mml:mn><mml:mo>,</mml:mo><mml:msup><mml:mrow><mml:mn>0.1</mml:mn></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:mfenced></mml:math>. You can set the first value, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://schemas.openxmlformats.org/officeDocument/2006/math"><mml:msub><mml:mrow><mml:mi>y</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msub></mml:math>, of the generated series to zero. Use the statsmodels.tsa.arima.model.ARIMA function from the statsmodels package to fit an ARIMA(1,1,1) model to the simulated data you have just generated...

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