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2018-07-04T16:28:45Z

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nemenman>Ilya at 14:00, 12 February 2018

2018-02-12T14:00:27Z

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{{PHYS212-2018}}

Here we start a new module, where we will explore how to model and solve dynamical systems in more detail. In this lecture we discussed a few important concepts in programming, some specific to Python, and some not.

# We will discuss the importance of encapsulating the code that you use repeatedly into either a script or a function.
# We will discuss the difference between scripts (no inputs and no outputs) and functions (have inputs and outputs).
# We will focus on book section 6.1 -- Writing your own functions, and we wrote our first functions -- various growth rates for bacterial growth and solvers of the corresponding differential equations.
# We will start talking about variable types, and importance of type checking, and how Python figures out which type is a variable that has been passed to a function; we will return to this later.
# We will write our own loadable modules, and will discuss the importance of using the reload function.
# Finally, we will discuss some common coding mistakes that we all do when working with python, and specifically:
## Appending list or arrays instead of pre-allocating arrays -- appending arrays causes creation of new arrays, and then copying numbers, which takes time.
## Doing loops instead of vectorizing your math and operating on arrays -- doing loops causes Python to do type checking of variables at every step of the way, which is costly.

Coding problem for you was: write a function to solve a quadratic equation, and think about how to make it bullet-proof, and give solutions gene if they are complex, or if they are degenerate. [https://docs.google.com/forms/d/e/1FAIpQLSeNvrPddCgvMfHdlSA8uYDddBFqLK81Rrr4l7jfozud6J7iww/viewform submit your work].

:Scripts for this Module:
::[[media:growthfunctions.py | GrowthFunctions]] -- module defining different growth functions.
::[[media:Integrators_v2.txt | Integrators]] -- module defining different integrators (Euler and Runge-Kutta second order).
::[[media:Module2_v2.txt | Module 2]] -- catch-all scripts I used during the class.

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Physics 212, 2018: Lectures 6 - Revision history

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nemenman>Ilya at 14:00, 12 February 2018