Manual Legend With Math Formulas

import numpy as np

from lets_plot import *

LetsPlot.setup_html()

# Define the functions
def f1(x):
    return np.sin(3*x) / (x * (np.cos(x) + 2))

def f2(x):
    return np.cos(x) / x

def f3(x):
    return np.exp(-x)

c = ['#FFB6C1', '#AAFFAA', '#ADD8E6']
p = (ggplot()
  + geom_vline(xintercept=0, size=0.4)   
  + geom_hline(yintercept=0, size=0.4)   
  + geom_function(fun=f1, xlim=[0.1, 12], color=c[0], size=2, 
                  n=300, manual_key=layer_key('sin(3x)\n--------\nx(cos(x) + 2)', size=3))
  + geom_function(fun=f2, xlim=[0.1, 12], color=c[1], 
                  n=300, manual_key=layer_key('cos(x) / x', size=3))
  + geom_function(fun=f3, xlim=[0.1, 12], color=c[2], 
                  n=300, manual_key=layer_key(r'\( e^{-x} \)', size=3))
  + scale_x_continuous(expand=[0, 0.2])
  + scale_y_continuous(limits=[-0.4, 1.0])
  + labs(
      x='x',
      y='f(x)',
      title='Mathematical Functions'
    )
  + theme_classic()
     
  + theme(
      # Titles, labels
      text=element_text(face='italic', family='Computer Modern'), 
      plot_title=element_text(size=20, hjust=0.05),
      axis_title=element_text(size=18),
      legend_text=element_text(size=18, vjust=0.5),
      # Legend
      legend_background=element_rect(size=1),
      legend_position=[0.95, 0.9], 
      legend_justification=[1, 1],
      # Axis, gridlines                 
      axis_line='blank', axis_ticks='blank',
      panel_grid_major=element_line(linetype='longdash'),
  )
  + theme(
      # Layout improvements
      panel_inset=4,
      plot_inset=0,
      axis_text=element_text(margin=0),
      axis_title=element_text(margin=0),
      plot_margin=16
  )
     
  + flavor_solarized_dark()   
  + ggsize(900, 500)   
)     

p