Lab: Plotting with Python

In this lab, you will develop a program to plot mathematical equations using Python.

Instructions

You should complete this lab individually.

Step 1: Review Starter Code

Download and review the starter code, consulting the documentation for these Python modules:

• argparse
• seaborn

Before running the starter code, you must install seaborn.

Next, use the --help option to see program’s command-line interface:

> python plot.py --help
usage: plot.py [-h] [--x-min X_MIN] [--x-max X_MAX] [--output OUTPUT] expr

Plot mathematical equations.

positional arguments:
  expr             A mathematical expression in terms of x

options:
  -h, --help       show this help message and exit
  --x-min X_MIN    The minimum x-value to display
  --x-max X_MAX    The maximum x-value to display
  --output OUTPUT  Name of the output file to save

Step 2: Implementation

Modify the starter code to support plotting $x, x^2, \text{ and } x^3$. This will involve calculating the corresponding y-value for each x-value, according to the expression specified by the user. By default, the program will save plots to output.png.

If implemented correctly, you should see output like:

> python plot.py x

> python plot.py "x**2"

> python plot.py "x**3"

Note: Quotation marks are used around "x**2" and "x**3", because the * character has a special meaning to the command-line shell.

Note: Do not change the visual styling of the graphs, or the autograder will get confused.

Optional: Support Arbitrary Expressions

Rather than hardcode the calculation of $x, x^2, \text{ and } x^3$, it is possible to support graphing any mathematical expression. I recommend implementing this functionality using the SymPy library. For example, you could interpret the expression typed by the user with sympify() and you could substitute values into the expression using subs().

A further benefit of using SymPy is that you can solve for an equation’s inverse. For example, this shows the plot of $\frac{1}{x-2}$ and its inverse:

> python plot.py "1/(x-2)"

Submit

Upload plot.py to Gradescope.

Learning Goals

• Evaluate equations in Python
• Graph equations in Python