Plotting on Python

Question

My program uses two functions f1(x) and f2(X) to plot data. for some reason no graph appears at the end:

def create_plot_data(f, xmin, xmax, n):
    """Computes and returns a tuple (xs, ys) where xs and ys are two
    sequences"""
    xs = []
    ys = []
    for i in range(n):
        x = xmin + i * (float((xmax - xmin))/ (n - 1))
        xs.append(x)
        y = f(x)
        ys.append(y)
    return xs, ys

def f1(x):
    """ Computes a function f1(x) which accepts an number x as input and
    returns f(x)"""
    f(x) = math.cos(2 * math.pi * x) * math.exp(-(x ** 2))
    return f(x)


def f2(X):
    """ Computes a function f2(x) which accepts an number x as input and
    returns f(x)"""
    f(x) = math.log(x + 2.1)
    return f(x)


def myplot():
    """Computes and returns plots of f1(x) and f2(x) using 1001 points for x
    ranging from -2 to +2."""
    import pylab
    import numpy as np
    f1data = create_plot_data(f1, -2, 2, 1001)
    f2data = create_plot-data(f2, -2, 2, 1001)
    pylab.plot(f1data[0], f1data[1], label = "f1(x)") #f1data[0] refers to first item in tuple {xs, ys}
    pylab.plot(f2data[0], f2data[1], "y", label = "f2(x)")
    pylab.legend(loc = "upper right")
    pylab.xlabel("x")
    pylab.savefig("plot.png")
    pylab.show()

can someone tell me how to edit this to as it appears on python please

Robᵩ · Accepted Answer · 2014-01-02 18:32:42Z

You have a number of errors in your program:

the math functions are not in scope. Add import math to the top of your file
python is case-senstive. Replace def f2(X) with def f2(x)
python does not create functions using the syntax f(x) = /code/. Replace f(x) = ... / return f(x) with y = ... / return y
You have a typo. Replace create_plot-data with create_plot_data.
Finally, to answer your question, you create several functions, but you never invoke them. You must invoke myplot(). Add these lines to the end of your file:

if __name__=="__main__":
   myplot()

The entire, corrected, program is here:

import math
def create_plot_data(f, xmin, xmax, n):
    """Computes and returns a tuple (xs, ys) where xs and ys are two
    sequences"""
    xs = []
    ys = []
    for i in range(n):
        x = xmin + i * (float((xmax - xmin))/ (n - 1))
        xs.append(x)
        y = f(x)
        ys.append(y)
    return xs, ys

def f1(x):
    """ Computes a function f1(x) which accepts an number x as input and
    returns f(x)"""
    y = math.cos(2 * math.pi * x) * math.exp(-(x ** 2))
    return y


def f2(x):
    """ Computes a function f2(x) which accepts an number x as input and
    returns f(x)"""
    y = math.log(x + 2.1)
    return y


def myplot():
    """Computes and returns plots of f1(x) and f2(x) using 1001 points for x
    ranging from -2 to +2."""
    import pylab
    import numpy as np
    f1data = create_plot_data(f1, -2, 2, 1001)
    f2data = create_plot_data(f2, -2, 2, 1001)
    pylab.plot(f1data[0], f1data[1], label = "f1(x)") #f1data[0] refers to first item in tuple {xs, ys}
    pylab.plot(f2data[0], f2data[1], "y", label = "f2(x)")
    pylab.legend(loc = "upper right")
    pylab.xlabel("x")
    pylab.savefig("plot.png")
    pylab.show()

if __name__=="__main__":
    myplot()

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