Log scale and symlog scale in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of log scale plot ticks

What will be the y-axis tick labels when using plt.yscale('log') on data ranging from 1 to 1000?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np
x = np.linspace(1, 10, 10)
y = np.linspace(1, 1000, 10)
plt.plot(x, y)
plt.yscale('log')
ticks = plt.gca().get_yticks()
print(ticks)

A [1.0, 2.0, 3.0, 4.0, 5.0]

B [1.0, 10.0, 100.0, 1000.0]

C [0.1, 1.0, 10.0, 100.0, 1000.0]

D [1.0, 5.0, 25.0, 125.0, 625.0]

💡 Hint

Think about how log scale places ticks at powers of 10.

Log scale places ticks at powers of 10 by default, so ticks include 1, 10, 100, 1000, etc.

❓ data_output

intermediate

Effect of symlog scale on negative values

Given the data y = [-100, -10, -1, 0, 1, 10, 100], what will be the y-axis limits after applying plt.yscale('symlog', linthresh=1)?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np
y = np.array([-100, -10, -1, 0, 1, 10, 100])
plt.plot(y)
plt.yscale('symlog', linthresh=1)
lims = plt.gca().get_ylim()
print(lims)

A (-110.0, 110.0)

B (-10.0, 10.0)

C (-1.0, 1.0)

D (-100.0, 100.0)

💡 Hint

Symlog scale extends limits slightly beyond data range to show linear region.

Symlog scale with linthresh=1 extends limits beyond data range to include linear region around zero, so limits are slightly larger than min and max data values.

❓ visualization

advanced

Identify the plot with symlog scale

Which plot correctly uses symlog scale to handle data with negative and positive values near zero?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np
x = np.linspace(-10, 10, 400)
y = x**3
plt.figure(figsize=(8, 4))
plt.subplot(1, 2, 1)
plt.plot(x, y)
plt.yscale('log')
plt.title('Log scale')
plt.subplot(1, 2, 2)
plt.plot(x, y)
plt.yscale('symlog', linthresh=100)
plt.title('Symlog scale')
plt.tight_layout()
plt.show()

A Neither plot uses symlog scale

B The left plot uses symlog scale

C The right plot uses symlog scale

D Both plots use symlog scale

💡 Hint

Symlog scale can show negative values near zero, log scale cannot.

The right plot uses symlog scale which handles negative and positive values near zero by combining linear and log scales. The left plot uses log scale which cannot handle negative values.

🧠 Conceptual

advanced

Why use symlog scale instead of log scale?

Which reason best explains why you would choose symlog scale over log scale in a plot?

A To display categorical data with labels

B To display only positive data with large range

C To display data with only zero values

D To display data with both negative and positive values including zero

💡 Hint

Log scale cannot show zero or negative values.

Symlog scale allows plotting data with negative, zero, and positive values by combining linear scale near zero and log scale away from zero.

🔧 Debug

expert

Identify the error in symlog scale usage

What error will this code produce and why?

import matplotlib.pyplot as plt
import numpy as np
x = np.linspace(-10, 10, 100)
y = x**2
plt.plot(x, y)
plt.yscale('symlog', linthresh=-1)
plt.show()

Matplotlib

import matplotlib.pyplot as plt
import numpy as np
x = np.linspace(-10, 10, 100)
y = x**2
plt.plot(x, y)
plt.yscale('symlog', linthresh=-1)
plt.show()

A ValueError because linthresh must be positive

B TypeError because y is not a list

C No error, plot displays correctly

D RuntimeWarning due to negative y values

💡 Hint

Check the parameter requirements for linthresh in symlog scale.

The linthresh parameter must be a positive number. Negative linthresh causes ValueError.