MANA624 - 7 months ago 46

Python Question

What is the best way to create a Sympy equation, do something like take the derivative, and then plot the results of that equation?

I have my symbolic equation, but can't figure out how to make an array of values for plotting. Here's my code:

`from sympy import symbols`

import matplotlib.pyplot as mpl

t = symbols('t')

x = 0.05*t + 0.2/((t - 5)**2 + 2)

nums = []

for i in range(1000):

nums.append(t)

t += 0.02

plotted = [x for t in nums]

mpl.plot(plotted)

mpl.ylabel("Speed")

mpl.show()

In my case I just calculated the derivative of that equation, and now I want to plot the speed

`x`

Answer

You can use `numpy.linspace()`

to create the values of the x axis (`x_vals`

in the code below) and `lambdify()`

.

```
from sympy import symbols
from numpy import linspace
from sympy import lambdify
import matplotlib.pyplot as mpl
t = symbols('t')
x = 0.05*t + 0.2/((t - 5)**2 + 2)
lam_x = lambdify(t, x, modules=['numpy'])
x_vals = linspace(0, 10, 100)
y_vals = lam_x(x_vals)
mpl.plot(x_vals, y_vals)
mpl.ylabel("Speed")
mpl.show()
```

_{(improvements suggested by asmeurer and MaxNoe)}

Alternatively, you can use sympy's `plot()`

:

```
from sympy import symbols
from sympy import plot
t = symbols('t')
x = 0.05*t + 0.2/((t - 5)**2 + 2)
plot(x, (t, 0, 10), ylabel='Speed')
```