## Thursday, October 12, 2017

### Adventures in Python: Plotting Sine and Cosine, The numpy Module

Adventures in Python:  Plotting Sine and Cosine, The numpy Module

This program will require that you have both numpy and matplotlib.  If you are working with Pythonista for the iOS, the two modules are included.  Other versions of Python require that you download matplotlib and numpy separately.

Pointers:

1. The module numpy works with functions with lists as arguments.  There is a math function associated with numpy.  See the section on numpy functions below.

2.  It is helpful to set up all the graphing parameters before showing the graph with pylplot.show().

3. Color strings are six digit hexadecimal integers with the format ‘#RRGGBB’ (R = red, G = green, B = blue)

4.  To turn the plot grid on, use pyplot.legend().  To turn on the legend on use pyplot.legend().  Labels are defined in pyplot.plot

Program:

# this will require matplotlib

# radians mode is the default
import matplotlib
from matplotlib import pyplot

# will need numpy to generate lists
import numpy

# we will need math module for pi
import math

# generate lists
x = numpy.linspace(-2*math.pi, 2*math.pi, 50)
# sin and cos are included in numpy
y1 = numpy.sin(x)
y2 = numpy.cos(x)
y3 = numpy.sin(x)+numpy.cos(x)
# alt for y3: numpy.add(y1,y2)

# the plot begins
pyplot.plot(x,y1,color = '#228b22', label = 'sin x')
pyplot.plot(x,y2,color = '#ffa500', label = 'cos x')
pyplot.plot(x,y3,color = '#919811', label = 'sin x + cos x')

# turn grid on
pyplot.grid(True)
# labels
pyplot.title('Trig Plots 007')
pyplot.xlabel('x')
pyplot.ylabel('y')
# turn legend box on
pyplot.legend()
# show the plot
pyplot.show()

Output:

Some Numpy Functions

numpy.add(list 1, list 2)    Adds two lists, element by element.

numpy.subtract(list 1, list 2)   Subtracts list 2 from list 1, element by element.

numpy.mutiply(list 1, list 2)   Multiplies two lists, element by element.

numpy.divide(list 1, list 2)    Divides list 1 by list 2, element by element.

numpy.power(list 1, list 2)    Calculates list 1**list 2.

numpy.maximum(list 1, list 2)  Takes the maximum of each respective pair.

numpy.minimum(list 1, list 2)   Takes the minimum of each respective pair.

numpy.round(list, number of decimal places)  Round each element.

Other element by element operations: (one list arguments – Radians is the default angle measure)

 numpy.square numpy.sqrt numpy.cbrt (cube root) numpy.absolute numpy.sin numpy.cos numpy.tan numpy.radians (convert to radians) numpy.asin numpy.acos numpy.atan numpy.degrees (covert to degrees) numpy.exp numpy.log (ln) numpy.real numpy.imag numpy.angle numpy.log10 (log) numpy.sinc numpy.i0 (Bessel first kind, order 0)

Until next time,

Eddie

This blog is property of Edward Shore, 2017.

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