openmmtools.utils.math_eval

openmmtools.utils.math_eval(expression, variables=None, functions=None)

Evaluate a mathematical expression with variables.

All the functions in the standard module math are available together with - step(x) : Heaviside step function (1.0 for x=0) - step_hm(x) : Heaviside step function with half-maximum convention. - sign(x) : sign function (0.0 for x=0.0)

Available operators are +, -, *, /, **, -x (negative), &, and, |, and or

The operators ``and`` and ``or`` operate BITWISE and behave the same as ``&`` and ``|`` respectively as this function is not designed to handle logical operations. If you provide sets, they must be as variables.

Parameters:

expressionstr

The mathematical expression as a string.

variablesdict of str: float, optional

The variables in the expression, if any (default is None).

functionsdict of str: callable function, optional

Additional functions to teach the math eval statement how to handle. Built-in functions are ‘step’, ‘step_hm’, and ‘sign’

Returns:

result

The result of the evaluated expression.

Examples

>>> expr = '-((x + ceil(y)) / z * 4 + step(-0.2))**2'
>>> vars = {'x': 1, 'y': 1.9, 'z': 3}
>>> math_eval(expr, vars)
-16.0