latex function and operations with fraction subscripts

[Markk]

sage: x = SR.symbol('x')
....: x_0 = SR.symbol('x_0')
....: logr = SR.symbol('L_x/x_0')
....: logr_ex = logr == log(x/x_0)
....: latex(logr_ex)
....: latex(logr_ex.solve(x)[0])
L_{\mathit{x/x}_{0}} = \log\left(\frac{x}{x_{0}}\right)

x = x_{0} e^{\frac{L_{x}}{x_{0}}}

The above attempt at using a symbol with a fraction in the subscript works (see first latex() result) until after an operation like solve(), which scrambles the symbol (second latex() result).

Variations of logr = SR.symbol('L_{x/x}_0') with braces also work until an operation such as logr_ex.solve(x) with the code above, which crash Maxima with the traceback excerpts:

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
/usr/lib/python3/dist-packages/sage/interfaces/interface.py in __init__(self, parent, value, is_name, name)
    731             try:
--> 732                 self._name = parent._create(value, name=name)
    733             except (TypeError, RuntimeError, ValueError) as x:
...

RuntimeError: ECL says: THROW: The catch MACSYMA-QUIT is undefined.

During handling of the above exception, another exception occurred:---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
/usr/lib/python3/dist-packages/sage/interfaces/interface.py in __init__(self, parent, value, is_name, name)
    731             try:
--> 732                 self._name = parent._create(value, name=name)
    733             except (TypeError, RuntimeError, ValueError) as x:

...

/usr/lib/python3/dist-packages/sage/interfaces/interface.py in __init__(self, parent, value, is_name, name)
    732                 self._name = parent._create(value, name=name)
    733             except (TypeError, RuntimeError, ValueError) as x:
--> 734                 raise TypeError(x)
    735
    736     def _latex_(self):

TypeError: ECL says: THROW: The catch MACSYMA-QUIT is undefined.

Looks like a bug, but maybe I've overlooked the correct way to define such symbols.

[Emmanuel Charpentier]

The /character cannot be part of a symbol’s name (not acepted by the Python interpreter). Try :

sage: logr = SR.symbol("logr", latex_name='L_{x/x_0}')
sage: x*logr
logr*x
sage: latex(x*logr)
L_{x/x_0} x

BTW (question of taste…), I’d rather use logr = SR.symbol("logr", latex_name=r'L_{\frac{x}{x_0}}')…

HTH,

​

[Samuel Lelievre]

Note: also asked on Ask Sage:

- Ask Sage question 63145

  How do you define a symbol with a quotient in the subscript?

  https://ask.sagemath.org/question/63145

[Markk]

Thanks, that does work. After (re-)implementing it I remembered why I didn't use latex_name--it doesn't seem to pickle:

sage: logr = SR.symbol('logr', domain='complex', latex_name=r'L_{x/x_0}')
....: latex(logr)
L_{x/x_0}

sage: import pickle
....: path_name = '/home/mark/'
....: pickle_file_name = path_name + 'node.p'
....: pickle_write = open(pickle_file_name, 'wb')
....: pickle.dump(logr, pickle_write)
....: pickle_write.close()

[exit and restart Sage]

sage: import pickle
....: path_name = '/home/mark/'
....: pickle_file_name = path_name + 'node.p'
....: pickle_read = open(pickle_file_name, 'rb')
....: some_expr = pickle.load(pickle_read)
....: pickle_read.close()
....: latex(some_expr)
\mathit{logr}

Reading the pickle in the same session does produce the correct results, however. Any ideas?

[dmo...@deductivepress.ca]

Thanks for reporting the unpickling issue. I opened trac ticket #34199 to address this.

I posted a fix there that should solve the latex_name problem for you if you can rebuild sagemath from source, but I do not know much about pickling and I think this is probably not the only attribute that is not unpickled, so the issue needs more thought.