如何使用LaTeX/amsmath和matplotlib？

Question

当我尝试在matplotlib中使用LaTeX amsmath软件包时，出现了许多不可理解的错误。有没有人能够做出这样的工作？如果是这样，我很乐意看到一个例子。

这里是我试过：

import matplotlib 
from matplotlib import pyplot 
from numpy import arange 

x= arange(5) 
y= x**1.5 

matplotlib.rc('text', usetex = True) 
matplotlib.rc('font', **{'family' : "sans-serif"}) 
params= {'text.latex.preamble' : [r'\usepackage{amsmath}']} 
pyplot.rcParams.update(params) 

fig= pyplot.figure(figsize=[10,7], dpi=120, facecolor=[1, 1, 1]) 
pyplot.plot(x, y, linewidth=2) 

pyplot.title(r"""$f(x)= 
    \begin{cases} 
    \a*x^\{1.5\}2 + c,& \text{if } -1 \leq x \leq 1\\ 
    0,    & \text{otherwise} 
    \end{cases}""") 

pyplot.show() 

此代码创建以下错误：

RuntimeError: LaTeX was not able to process the following string: 
' \\\\begin{cases}' 
Here is the full report generated by LaTeX: 

This is pdfTeX, Version 3.14159265-2.6-1.40.18 (MiKTeX 2.9.6300 64-bit) 
entering extended mode 
(1727d2fa12a0305b2ddc30e92e4e21fa.tex 
LaTeX2e <2017-04-15> 
Babel <3.9r> and hyphenation patterns for 75 language(s) loaded. 
("C:\Program Files\MiKTeX 2.9\tex\latex\base\article.cls" 
Document Class: article 2014/09/29 v1.4h Standard LaTeX document class 
("C:\Program Files\MiKTeX 2.9\tex\latex\base\size10.clo")) 
(C:\Users\s117250\AppData\Roaming\MiKTeX\2.9\tex\latex\type1cm\type1cm.sty) 
("C:\Program Files\MiKTeX 2.9\tex\latex\base\textcomp.sty" 
("C:\Program Files\MiKTeX 2.9\tex\latex\base\ts1enc.def")) 
("C:\Program Files\MiKTeX 2.9\tex\latex\amsmath\amsmath.sty" 
For additional information on amsmath, use the `?' option. 
("C:\Program Files\MiKTeX 2.9\tex\latex\amsmath\amstext.sty" 
("C:\Program Files\MiKTeX 2.9\tex\latex\amsmath\amsgen.sty")) 
("C:\Program Files\MiKTeX 2.9\tex\latex\amsmath\amsbsy.sty") 
("C:\Program Files\MiKTeX 2.9\tex\latex\amsmath\amsopn.sty")) 
("C:\Program Files\MiKTeX 2.9\tex\latex\geometry\geometry.sty" 
("C:\Program Files\MiKTeX 2.9\tex\latex\graphics\keyval.sty") 
("C:\Program Files\MiKTeX 2.9\tex\generic\oberdiek\ifpdf.sty") 
("C:\Program Files\MiKTeX 2.9\tex\generic\oberdiek\ifvtex.sty") 
("C:\Program Files\MiKTeX 2.9\tex\generic\ifxetex\ifxetex.sty") 
("C:\Program Files\MiKTeX 2.9\tex\latex\geometry\geometry.cfg") 

Package geometry Warning: Over-specification in `h'-direction. 
    `width' (5058.9pt) is ignored. 


Package geometry Warning: Over-specification in `v'-direction. 
    `height' (5058.9pt) is ignored. 

) (1727d2fa12a0305b2ddc30e92e4e21fa.aux) 
("C:\Program Files\MiKTeX 2.9\tex\latex\base\ts1cmr.fd") 
*geometry* driver: auto-detecting 
*geometry* detected driver: dvips 
! Missing $ inserted. 
<inserted text> 
       $ 
l.12 ...0000}{15.000000}{\sffamily \begin{cases} 
                } 

! LaTeX Error: \begin{cases} on input line 12 ended by \end{document}. 

See the LaTeX manual or LaTeX Companion for explanation. 
Type H <return> for immediate help. 
... 

l.13 \end{document} 

(1727d2fa12a0305b2ddc30e92e4e21fa.aux) 
! You can't use `\end' in internal vertical mode. 
\enddocument ... \endgroup \deadcycles \z@ \@@end 

l.13 \end{document} 


! LaTeX Error: \begin{cases} on input line 12 ended by \end{document}. 

See the LaTeX manual or LaTeX Companion for explanation. 
Type H <return> for immediate help. 
... 

l.13 \end{document} 

! Missing } inserted. 
<inserted text> 
       } 
l.13 \end{document} 

! Missing \right. inserted. 
<inserted text> 
       \right . 
l.13 \end{document} 

! Missing $ inserted. 
<inserted text> 
       $ 
l.13 \end{document} 

) 
! Emergency stop. 
<*> ./1727d2fa12a0305b2ddc30e92e4e21fa.tex 

No pages of output. 
Transcript written on 1727d2fa12a0305b2ddc30e92e4e21fa.log. 

Answer 1

你需要确保的字符串是有效的乳胶。然后下面应该工作：

import matplotlib 
from matplotlib import pyplot 
from numpy import arange 

x= arange(5) 
y= x**1.5 

matplotlib.rc('text', usetex = True) 
matplotlib.rc('font', **{'family' : "sans-serif"}) 
params= {'text.latex.preamble' : [r'\usepackage{amsmath}']} 
pyplot.rcParams.update(params) 

fig= pyplot.figure(figsize=[10,7], dpi=120, facecolor=[1, 1, 1]) 
pyplot.plot(x, y, linewidth=2) 

pyplot.title(r"$f(x)= \begin{cases} a\times x^{1.5}2 + c,& \text{if } -1 \leq x \leq 1\\ 0, & \text{otherwise} \end{cases}$") 

pyplot.show() 

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