Matplotlib / Matlab log axis plots
In Python Matplotlib or Matlab, making a plot with log-scaled (instead of default linear-scaled) axes can use the functions like “loglog()”, “semilogx()”, or “semilogy()”. Here we show the more general object-oriented syntax for each of a 2-D line “plot()” and 2-D pseudocolor “pcolor()” and then set the axes scale properties.
We arbitrarily use log abscissa scale and linear ordinate scale, but the same syntax applies to other combinations.
Python
2-D line plot:
import numpy as np
from matplotlib.pyplot import figure, show
x = np.logspace(0, 10, 100)
y = np.log(x)**2
fg = figure()
ax = fg.gca()
ax.plot(x, y)
ax.set_xscale('log')
ax.set_xlabel('x')
ax.set_ylabel('y')
show()pseudocolor pcolormesh(): observe the stretching of the ticks along the y-axis. In some cases it’s helpful to set the axis limits manually to avoid whitespace past the last data point.
import numpy as np
from matplotlib.pyplot import figure, show
d = np.random.rand(10, 10)
x = np.linspace(1, 10, d.shape[0])
y = np.logspace(0, 1, d.shape[1])
fg = figure()
ax = fg.gca()
ax.pcolormesh(x, y, d)
ax.set_yscale('log')
ax.set_ylim(y[0], y[-1])
ax.set_xlabel('x')
ax.set_ylabel('y')
show()Matlab
2-D line plot:
x = logspace(0, 10, 100);
y = log(x).^2;
fg = figure();
ax = axes(fg);
plot(ax, x, y);
ax.XScale = 'log';
xlabel(ax, 'x');
ylabel(ax, 'y');pseudocolor pcolor(): observe the stretching of the ticks along the y-axis. In some cases it’s helpful to set the axis limits manually to avoid whitespace past the last data point.
d = rand(10, 10);
x = linspace(1, 10, size(d, 1));
y = logspace(0, 1, size(d, 2));
fg = figure();
ax = axes(fg);
pcolor(ax, x, y, d);
ax.YScale = 'log';
xlabel(ax, 'x');
ylabel(ax, 'y');