Expression variable

This variable describes a general mathematical expression of known parameters and predicted variables stemming either from surrogates or from any previously defined variable. This variable type is the most flexible. However, its distribution is not determined analytically, but only through sampling from the posterior distribution(s) of the input variables and evaluating the expression of each of the samples. For linear or quadratic expressions it is generally advisable to use the more specialized variables instead.

name (str)

The name of the variable under which it can be addressed by other variables or objectives. The name must be distinct from any surrogate name.

Default: 'v'

expression (str)

String defining a mathematical expression of other variables and parameters of the design space and environment. The expression can contain numbers as either integers or floating-point reals in standard or exponential notation (0.0012 or 1.2E-3) as well as the constants E (Euler constant) and PI (\(\pi\)). Parameter names may not start with the capital letters “E” nor “PI”. Supported operations are +, -, *, /, ^, supported single-argument functions are sqrt, sinh, sin, asinh, asin, cosh, cos, acosh, acos, tanh, tan, atanh, atan, exp, log10, log, erfinv, erf, abs, trunc, round, sign, and supported multi-argument functions are max, min.

Default: '0'

Example

Expression with trigonometric functions.

'sin(2*PI*variable1)^2 + cos(2*PI*variable2)^2'