Q: Is there a sympy defaults file, like matplotlib has ~/matplotlib/.matplotlibrc? Is there a sympy defaults file, like matplotlib has ~/matplotlib/.matplotlibrc?
Presently, the default LaTeX output for the following code uses smallmatrix, which is too small:
>>> mat = Matrix([[0 1], [1 0]])
>>> latex(mat)
\left[\begin{smallmatrix} ...

I would like it to use matrix by default. For now, I do it with:
>>> latex(mat, mat_str='matrix')
\left[\begin{matrix} ...

I would like to have the ability to set a default without having to use mat_str='matrix'

A: You could always just write your own small wrapper to latex
def latex(*args, **kwargs):
    kwargs.setdefault('mat_str', 'matrix')
    sympy.latex(*args, **kwargs)

If you want to change the behavior of init_printing, there's an open issue for it. 

A: Doesn't look like sympy reads any defaults files. Matrices types are hardcoded in /sympy/printing/latex.py with the following comment:

mat_str: Which matrix environment string to emit. "smallmatrix", "matrix",
  "array", etc. Defaults to "smallmatrix" for inline mode, "matrix" for
  matrices of no more than 10 columns, and "array" otherwise.

You can change hardecoded defaults by modifying the following fragment (currently at line 1169):
mat_str = self._settings['mat_str']
        if mat_str is None:
            if self._settings['mode'] == 'inline':
                mat_str = 'smallmatrix'
            else:
                if (expr.cols <= 10) is True:
                    mat_str = 'matrix'
                else:
                    mat_str = 'array'

Just replace 'smallmatrix' with 'matrix' and use mat_str parameter if you need to override it.
