In Jupyter Notebook i would like to define a equation, differentiate and plot the equation.
import sympy as sp
from IPython.display import display
sp.init_printing()
import matplotlib.pyplot as plt
import numpy as np
x = sp.symbols('x')
def func(x):
a= sp.sympify("4/5")
return (x**3+a*x**2)
display(func(x))
def dfunc(x):
a = sp.diff(func(x),x)
return a
display(dfunc(x))
x = np.linspace(-10,10,20)
plt.plot(x,func(x))
plt.plot(x,dfunc(x)) # doesn't work
display(dfunc(x)) shows the wanted function but plt.plot(x,dfunc(x)) returns the error message ValueError: cannot derive by this array
Does anyone know how to get the plot?
(It also doesn't work with sp.integrate(func(x),x) instead of sp.diff(func(x),x). Just another error message is returned ValueError: Invalid limits given: ...)
Many thanks in advance.
Matthias
You can use the SymPy plot function rather than the matplotlib one. The matplotlib plot function expects arrays as inputs whereas the sympy one accepts sympy expressions (and then calculates values to make the arrays for matplotlib):
In [36]: import sympy as sym
In [37]: a = sym.Rational(4, 5)
In [38]: x = sym.Symbol('x')
In [39]: f = x**3 + a*x**2
In [40]: f
Out[40]:
2
3 4⋅x
x + ────
5
In [41]: f.diff(x)
Out[41]:
2 8⋅x
3⋅x + ───
5
In [42]: sym.plot(f.diff(x))