# Recent content by Edgardo

1. ### Quantum Springer discount code CYBERWEEK19 - English IT books only 7 Euro

Use the discount code CYBERWEEK19 to purchase English IT eBooks from Springer online for only 7 Euro. Go to the checkout and enter the code. Afterwards, you can proceed browsing the book list and it automatically shows if the code was applied. Note: At the checkout read again if the discount...
2. ### Analysis Springer math books 40% off till Nov 30

Springer math books are 40% off till Nov 30. Coupon code is MATH19PE. I bought Linear Algebra by Axler , the analysis books by Pugh and Abbott. Any further recommendations for good books?
3. ### I Merging neutron stars

5 minute video by Veritasium (Derek Muller) on the event:
4. ### I Contradiction vs contraposition

You are asking about the difference between "Proof by contraposition" and "Proof by contradiction", and here is an example. To prove p \rightarrow q: - In proof by contraposition you start by assuming that \neg q is true and derive the statement \neg p. Here, the path is clear, i.e. you start...
5. ### B Help simplifying an equation

I typed your equation and "simplify" into wolframalpha, and this is what I got It has a simpler looking form for x, d and theta real.
6. ### Neural networks and the derivatives of the cost function

Here is a derivation from stats.stackexchange that you may find helpful. It is basically about the chain rule for derivatives.
7. ### AlphaGo success

Result of match 4: Article by GoGameGuru Article by Wired
8. ### AlphaGo success

Great article on the third match between AlphaGo and LeeSedol.
9. ### AlphaGo success

Result of the second match between AlphaGo and Lee Sedol.
10. ### YouTube Classics, Part Deux

Look how beautiful the ostrich's running technique is! My favorite part is the left and right swerving, but why does the ostrich do it?
11. ### Google's AI beats world Go champion

Go has been considered one of the games in which the human is superior to any AI. However in a first match Google's AI has beaten world Go champion Lee Se-dol. Earlier this year the AI beat the European Go champion.
12. ### I The Hamiltonian

Right-click on the math error, go to Math Settings -> Math Renderer and try e.g. HTML-CSS (or some other renderer).
13. ### Insight/Intuition into rotations in R²

Here is a good explanation: http://mathforum.org/library/drmath/view/74063.html
14. ### Summation Convention – Substitution Rule

Try to get an intuitive feeling for what the Kronecker-Delta \delta_{ij} does. Consider this sum: \sum_{j=1}^{n} c_j = c_1 + c_2 + \dots + c_n Now observe what happens if we multiply with the Kronecker-Delta: \sum_{j=1}^{n} \delta_{ij} c_j = \delta_{i1} c_1 + \delta_{i2}c_2 + \dots +...
15. ### Summation with no argument

For a sequence (a_n)_{n \in \mathbb{N}} you can form the series \sum_{n=0}^\infty a_n = a_0 + a_1 + a_2 + \dots. If you take the sequence a_n = 1 and plug it into the expression above, then you get the series \sum_{n=0}^\infty a_n = \sum_{n=0}^\infty 1 = 1 + 1 + 1 \dots . Or consider the...