Jessie Cotton - 6 months ago 36

Python Question

So far I have managed to find the particular solution to this equation for any given mass and drag coefficient. I have not however found a way to plot the solution or even evaluate the solution for a specific point. I really want to find a way to plot the solution.

`from sympy import *`

m = float(raw_input('Mass:\n> '))

g = 9.8

k = float(raw_input('Drag Coefficient:\n> '))

f = Function('f')

f1 = g * m

t = Symbol('t')

v = Function('v')

equation = dsolve(f1 - k * v(t) - m * Derivative(v(t)), 0)

C1 = Symbol('C1')

C1_ic = solve(equation.rhs.subs({t:0}),C1)[0]

equation = equation.subs({C1:C1_ic})

Answer

Import these libraries (seaborn just makes the plots pretty).

```
from matplotlib import pyplot as plt
import seaborn as sns
import numpy as np
```

Then tack this onto the end. This will plot time, t, against velocity, v(t).

```
# make a numpy-ready function from the sympy results
func = lambdify(t, equation.rhs,'numpy')
xvals = np.arange(0,10,.1)
yvals = func(xvals)
# make figure
fig, ax = plt.subplots(1,1,subplot_kw=dict(aspect='equal'))
ax.plot(xvals, yvals)
ax.set_xlabel('t')
ax.set_ylabel('v(t)')
plt.show()
```

I get a plot like this for a mass of 2 and a drag coefficient of 2.