erf x
This calls Python's built-in math.erf function, which computes the error function of x.
math.erf
i1 : erf toPython 0 o1 = 0.0 o1 : PythonObject of class float
i2 : erf toPython 1 o2 = 0.8427007929497149 o2 : PythonObject of class float
The source of this document is in Python/doc/special.m2:26:0.