# Operators ## Pre-defined First, note that pretty much any valid Julia function which takes one or two scalars as input, and returns on scalar as output, is likely to be a valid operator[^1]. A selection of these and other valid operators are stated below. **Binary** - `+` - `-` - `*` - `/` - `^` - `max` - `min` - `mod` - `cond` - Equal to `(x, y) -> x > 0 ? y : 0` - `greater` - Equal to `(x, y) -> x > y ? 1 : 0` - `logical_or` - Equal to `(x, y) -> (x > 0 || y > 0) ? 1 : 0` - `logical_and` - Equal to `(x, y) -> (x > 0 && y > 0) ? 1 : 0` **Unary** - `neg` - `square` - `cube` - `exp` - `abs` - `log` - `log10` - `log2` - `log1p` - `sqrt` - `sin` - `cos` - `tan` - `sinh` - `cosh` - `tanh` - `atan` - `asinh` - `acosh` - `atanh_clip` - Equal to `atanh(mod(x + 1, 2) - 1)` - `erf` - `erfc` - `gamma` - `relu` - `round` - `floor` - `ceil` - `round` - `sign` ## Custom Instead of passing a predefined operator as a string, you can define with by passing it to the `pysr` function, with, e.g., ```python PySRRegressor( ..., unary_operators=["myfunction(x) = x^2"], binary_operators=["myotherfunction(x, y) = x^2*y"], extra_sympy_mappings={ "myfunction": lambda x: x**2, "myotherfunction": lambda x, y: x**2 * y, }, ) ``` Make sure that it works with `Float32` as a datatype (for default precision, or `Float64` if you set `precision=64`). That means you need to write `1.5f3` instead of `1.5e3`, if you write any constant numbers, or simply convert a result to `Float64(...)`. PySR expects that operators not throw an error for any input value over the entire real line from `-3.4e38` to `+3.4e38`. Thus, for invalid inputs, such as negative numbers to a `sqrt` function, you may simply return a `NaN` of the same type as the input. For example, ```julia my_sqrt(x) = x >= 0 ? sqrt(x) : convert(typeof(x), NaN) ``` would be a valid operator. The genetic algorithm will preferentially selection expressions which avoid any invalid values over the training dataset. [^1]: However, you will need to define a sympy equivalent in `extra_sympy_mapping` if you want to use a function not in the above list.