Making a module

• Previous programs: much repetitive code (esp. solver)
• DRY (Don't Repeat Yourself) principle: no copies of code
• A change needs to be done in one and only one place
• Module = just a file with functions (reused through import)
• Let's make a module by putting these functions in a file:

• solver
• verify_three_steps
• verify_discrete_solution
• explore
• define_command_line_options
• read_command_line
• main (with convergence rates)
• verify_convergence_rate