[FIXED] Make a label both Italic and Bold style in Matplotlib with stix font

Issue

I am trying to generate a plot with matplotlib and I use the 'stix' font (rcParams['mathtext.fontset'] = 'stix') in order to have smooth font size transitions from text to math text. However, some of my math symbols I want to be Italic (scalar values) and some to be Italic AND Bold (tensors). I do not want to go through the solution of using Latex rendering cause then other things are messed up.

I will give you a small example that depicts the problem:

from numpy import *
from matplotlib.pyplot import * 

# Chaning font to stix
rcParams['mathtext.fontset'] = 'stix'

# Some data to constract this plotting example
datax=[0,1,2]
datay=[8,9,10]
datay2=[8,15,10]

fig, ay = subplots()

ay.plot(datax, datay, color="0.", ls='-', label= r"$F_{\alpha}$")
ay.plot(datax, datay2, color="0.", ls='-', label=r"$\mathbf{F_{\alpha}}$")

# Now add the legend with some customizations.
legend = ay.legend(loc='left', shadow=True)

#frame = legend.get_frame()
#frame.set_facecolor('0.90')
xlabel(r"x label",fontsize=18)
ylabel(r'y label', fontsize=18)
grid()

show()

If you run the code the first label is Italic and the second label is Bold. How could I achieve the second label to be Bold AND Italic?

Problem with math text to be Italic and bold

Solution

A few more specific mathtext params are needed:

from numpy import *
from matplotlib.pyplot import *

# Changing font to stix; setting specialized math font properties as directly as possible
rcParams['mathtext.fontset'] = 'custom'
rcParams['mathtext.it'] = 'STIXGeneral:italic'
rcParams['mathtext.bf'] = 'STIXGeneral:italic:bold'

# Some data to construct this plotting example
datax=[0,1,2]
datay=[8,9,10]
datay2=[8,15,10]

fig, ay = subplots()

ay.plot(datax, datay, color="0.", ls='-', label= r"$\mathit{F_{\alpha}}$")
ay.plot(datax, datay2, color="0.", ls='-', label=r"$\mathbf{F_{\alpha}}$")

# Now add the legend with some customizations.
legend = ay.legend(loc='left', shadow=True)

# Using the specialized math font again
xlabel(r"$\mathbf{x}$ label",fontsize=18)
ylabel(r'y label', fontsize=18)
grid()

show()

Note that I used the mathbf in an axis label, too. Would probably change the rest of the label to a STIX font, which you can define a non-italic-non-bold case of: see the docs under 'Custom fonts'.

There are also at least two examples in the matplotlib Gallery that might help: one looking at font families and another reminding us which STIX fonts are which.

Answered By - cphlewis