Python - Lambda Week: Plotting Functions
Welcome to Python Week! This we we're going to cover calculus and the keyword lambda.
Note: All Python scripts presented this week were created using a TI-NSpire CX II CAS. As of June 2022, the lambda keyword is available on all calculators (in the United States) that have Python. If you are not sure, please check your calculator manual.
Plotting Functions
We can use the line:
f=eval("lambda x:"+input("f(x) = "))
for multiple applications. Remember, lambda functions are not defined so that they can be used outside of the Python script it belongs to but it lambda functions are super useful!
This code is specific to the Texas Instruments calculators (TI-Nspire CX II (CAS), TI-84 Plus CE Python, TI-83 CE Premium Python Edition, but NOT the TI-82 Advanced Python). For other calculators, HP Prime, Casio fx-CG 50, Casio fx-9750GIII/9860GIII, Numworks, or computer Python, apply similar language.
plotlam.py: Plotting with Lambda
from math import *
import ti_plotlib as plt
# this is for the TI calcs
# other calculators will use their own plot syntax
print("The math module is imported.")
# input defaults to string
# use the plus sign to combine strings
f=eval("lambda x:"+input("f(x) = "))
# set up parameters
x0=eval(input("x min = "))
x1=eval(input("x max = "))
# we want n to be an integer
n=int(input("number of points = "))
# calculate step size
h=(x1-x0)/n
# calculate plot lists
x=[]
y=[]
i=x0
while i<=x1:
x.append(i)
y.append(f(i))
i+=h
# choose color (not for Casio fx-9750/9850GIII)
# colors are defined using tuples
colors=((0,0,0),(255,0,0),(0,128,0),(0,0,255))
print("0: black \n1: red \n2: green \n3: blue")
c=int(input("Enter a color code: "))
# plot f(x)
# auto setup to x and y lists
plt.auto_window(x,y)
# plot axes
plt.color(128,128,128)
plt.axes("axes")
# plot the function
plt.color(colors[c])
plt.plot(x,y,".")
plt.show_plot()
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