1. A tangible computer-readable medium having recorded thereon statements and instructions for execution by a computer of a method to generate at least one mathematical expression describing a performance characteristic of a system, the system associated with variables and with pre-determined data related to the performance characteristic of the system, the method comprising steps of: generating at least one initial mathematical expression having a pre-defined canonical form and being a function of the variables, the at least one initial mathematical expression having operators operating on the variables, the operators being selected from a pre-defined group of operators, the at least one initial mathematical expression describing the performance characteristic of the system; wherein, the variables of the system are representable as a vector {right arrow over (x)} and the canonical form of an expression F({right arrow over (x)}) is representable as F ⁡ ( x ) = w offset + ∑ i = 0 n ⁢ w i × f i ⁡ ( x ) × NL i ⁡ ( x ) , “n” being an integer, w offset , being an offset value, w i being weights, f i (x) including at least one of a polynomial function of the variables and a rational function of the variables, and NL i ({right arrow over (x)}) being a non-linear function of the variables, with NL 0 (x)=1; generating calculated data using the at least one initial mathematical expression; calculating an output of a goal function in accordance with the pre-determined data and the calculated data; determining that the goal function is outside a pre-defined range; and iteratively performing the following steps a-c until an additional output of the goal function is within the pre-defined range: a. modifying at least one input mathematical expression in accordance with a search algorithm to produce at least one modified mathematical expression having the canonical form and being a function of the variables, the search algorithm to search at least the pre-defined group of operators to identify operators with which to modify the at least one input mathematical expression, the at least one input mathematical expression being the at least one initial mathematical expression in a first iteration of steps a-c, the at least one input mathematical expression being the at least one modified mathematical expression in subsequent iterations of steps a-c; b. generating additional calculated data using the at least one modified mathematical expression; and c. calculating the additional output of the goal function based on the additional calculated data and the pre-determined data.