Practical application of the dot product

I recently had to write an algorithm to decide whether two trains (whose movement directions are known) are moving towards each other or not.

When two trains move towards each other the angle between their direction vectors is larger than 90 degrees. If the track was a straight line the angle would be close to 180 degrees, but tracks are not always straight.

I used the dot (scalar) product as follows:

1. Calculate the dot product of the train direction vectors. This is equal to cos(angle).
2. If 90 < angle <= 180 (-1 =< cos(angle) < 0), the two trains are moving towards each other

Note 1: If the track is bending more than 90 degrees, this algorithm will not work:

Note 2: If the trains have passed each other just using the dot product won't work, you also have to check whether the trains are in front of each other (let that be another blog post):

How to respond to questions of novice engineers

When a novice engineer comes to you with a technical question, your first reponse should not be answering the question at hand but asking "what are you trying to accomplish" because most of the time the novice will have gaps in his understanding of the job to be done. Based on that misunderstanding, he will try to solve some technical problem, get stuck and come to you for guidance.

By clarifying the higher level goal to be reached, you can be sure that the question is indeed meaningful and answering it will be productive.

Further reading: Difference between novice and experienced engineers

Music: Hallelujah - Pentatonix

Keeping motivation after lots of failures

Software development means getting stuck a lot of times where all your attempts at moving forward result in failure. This affects my motivation and after enough failures, I feel desperate and don't want to touch the project anymore.

One way to overcome this deadlock is to do smaller things with guaranteed success. For example, I improve documentation, draw prettier graphs, make more detailed plans. Scoring little victories shortens my procastination period and I gain enough enthusiasm to tackle the beast.

The 7 Habits of Highly Effective Artists

Rooting & Kiosk mode in Android 4.4.2 (KitKat)

Useful links for rooting & kiosk mode in Android 4.4.2 (KitKat):

---root---
https://www.kingoapp.com/root-tutorials/how-to-root-android-4.4.htm

---startup---
https://stackoverflow.com/questions/6391902/how-do-i-start-my-app-on-startup
https://stackoverflow.com/questions/10428510/how-to-start-launch-application-at-boot-time-android
https://android.stackexchange.com/questions/98276/open-an-app-on-startup-after-booting

---kiosk---
https://stackoverflow.com/questions/21363132/enabling-kioskmode-in-android-4-4-2-with-root