hu-guanwei/gradient-descent-vis

Udacity C++ project

Gradient Descent Visualization

Capstone Option 1

This is a 2d gradient descent algorithm simulator where multiple balls with possibly different initial positions are rolling down the landscape surface. The background brightness indicate the landscape surface value: The darker, the lower. The balls will go from random initial positions towards the position of lowest landscape surface value. Multi-threading is used to concurrently display and update positions of balls.

Library opencv is needed.

Running the code

• To compile the code mkdir build && cd build cmake .. make

• To start the application GUI, run./gradient_descent_viz

  • When the GUI is running:

    • press key q to quit the GUI. (The simulation is still running with printing to console. CTRL+C to stop the simulation)

    • press key r to reset the positions of balls randomly.

Code structure

• src/Graphics.h/Graphics.cpp: display landscape surface and balls position
• src/Ball.h/Ball.cpp: update the position of a ball by going along the gradient of landscape surface

Rubric

Object Oriented Programming

Criteria	Meets Specifications	files
The project uses Object Oriented Programming techniques.	The project code is organized into classes with class attributes to hold the data, and class methods to perform tasks.	see Ball.h, Ball.cpp, Graphics.h, Graphics.cpp
Classes use appropriate access specifiers for class members.	All class data members are explicitly specified as public, protected, or private.	see Ball.h, Graphics.h

Memory Management

Criteria	Meets Specifications	files and line numbers
The project makes use of references in function declarations.	At least two variables are defined as references, or two functions use pass-by-reference in the project code.	Ball.cpp line 10, main.cpp line 35; Graphics.cpp line 55
The project uses smart pointers instead of raw pointers.	The project uses at least one smart pointer: unique_ptr, shared_ptr, or weak_ptr. The project does not use raw pointers.	std::vector<std::shared_ptr<Ball>> _balls in Graphics.h line 14

In Ball.cpp line 10

void Ball::simulate(std::mutex &mu)

In main.cpp line 35

	ts.emplace_back(&Ball::simulate, b, std::ref(mu));

In Graphics.cpp line 55

void Graphics::fillLandscapeWith(const std::function<float(float, float)> &f)

Concurrency

Criteria	Meets Specifications	files and line numbers
The project uses multithreading	The project uses multiple threads in the execution.	main.cpp line 33-36
A mutex or lock is used in the project	A mutex or lock (e.g. std::lock_guard or `std::unique_lock) is used to protect data that is shared across multiple threads in the project code.	Ball.cpp line 28-34

In main.cpp

33    for (auto &b: balls) {
34        // simulate each ball in a different thread
35        ts.emplace_back(&Ball::simulate, b, std::ref(mu));
36    }

In Ball.cpp

28      mu.lock(); 
29      std::cout << "thread id\t: ";
30      std::cout << std::this_thread::get_id() << std::endl;
31      std::cout << "gradient norm\t: ";
32      std::cout << sqrt(pow(dx, 2) + pow(dy, 2)) << std::endl; 
33      std::cout << "===================================" << std::endl;
34      mu.unlock();   

This is to ensure console outputs will not be interleaved. (The variablestd::mutex mu is defined in main.cpp.)