dynamic latex code in a matplotlib title

Question

I am working on dynamic plots on jupyter with matplotlib, which means in a for loop each different cycle provides a different plot as in the example below

import matplotlib.pyplot as plt
import numpy as np
import time
import matplotlib as mpl
mpl.rcParams['lines.linewidth'] = 2
plt.ion()
%matplotlib notebook

x = np.arange(-10, 10, 0.01)

fig = plt.figure(figsize = (12, 7))
ax = fig.add_subplot(111)
ax.grid()
plt.show()
for j in range(1,5):
    ax.set_title(r"%6.2f    $y = \frac{\sin{(\pi x j)}}{(\pi x j)}$" % j)
    y = np.sin( np.pi*x*j )/( np.pi*x*j )
    line, = ax.plot(x, y, 'b')
    fig.canvas.draw()
    time.sleep(1)
    if j != 4:
        line.remove()

The line "ax.set_title" provides the title which has both a constant latex code and a number that changes over the time. My issue is that I can change a number in the title out of the latex code but I really don't know how to change a piece INSIDE the latex code.

In the previous example, for each different loop, I would like not only a different plot but also a title with a different latex code which provides a different result as reported here

Is there anyone who can suggest me anything about it?

@ImportanceOfBeingErnest - only because you used `.format()`. The OP is using `%` formatting and the second answer to the question I linked shows a perfectly valid solution: `r"%(j)6.2f $y = \frac{\sin{(\pi x %(j)6.2f)}}{(\pi x %(j)6.2f)}$" % {'j': j}` — Craig, Nov 25 '17 at 19:03

ImportanceOfBeingErnest · Accepted Answer · 2017-11-25T19:10:55.460

2

It makes sense to use the format notation.
Then you need to escape all curly brackets that need to be part of the MathText string.

plt.title(r"$y = \frac{{\sin{{({j}\pi)}}}}{{({j}\pi)}}$".format(j=3.14159265359))

To format the numbers in the format notation, you can define the number of decimal places ({j:.3f}) or use the general number format ({j:g}).

plt.title(r"$y = \frac{{\sin{{({j:.3f}\pi)}}}}{{({j:g}\pi)}}$".format(j=3.14159265359))

edited Nov 25 '17 at 19:10

answered Nov 25 '17 at 18:48

ImportanceOfBeingErnest

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great time for f-strings too! – Paul H Nov 25 '17 at 18:49
well wait, can you combine r- and f-strings? – Paul H Nov 25 '17 at 18:50
@PaulH Well, you would not need `r""` because backslashes can be escaped "\\". But since I rarely ever write code for pure python 3, so I've never used `f""`. – ImportanceOfBeingErnest Nov 25 '17 at 18:55
Almost there. The only problem is that your code provides me 10 decimal digits, how can I show only two of them? – Stefano Fedele Nov 25 '17 at 19:02
1

@StefanoFedele change `{j}` to `{j:0.2f}` (0.2 = two decimal places, f = floating point) – Paul H Nov 25 '17 at 19:38

dynamic latex code in a matplotlib title

1 Answers1