XLfit

The QMSys GUM Software is suitable for the analysis of the uncertainty of physical measurements, chemical analyses and calibrations. The software uses three different methods to calculate the measurement uncertainty. GUF Method for linear models, this method is applied to linear and quasi-linear models and corresponds to the GUM Uncertainty Framework. The software calculates the partial derivatives (the first term of a Taylor series) to determine the sensitivity coefficients of the equivalent linear model and then calculates the combined standard uncertainty in accordance with the Gaussian error propagation law. GUF Method for nonlinear models, this method is provided for nonlinear models with the symmetric distribution of the result quantities. In this method, a series of numerical methods are used, e.g. nonlinear sensitivity analysis, second and third-order sensitivity indices, quasi-Monte Carlo with Sobol sequences.

NLREG is a powerful statistical analysis program that performs linear and nonlinear regression analysis, surface and curve fitting. NLREG determines the values of parameters for an equation, whose form you specify, that cause the equation to best fit a set of data values. NLREG can handle linear, polynomial, exponential, logistic, periodic, and general nonlinear functions. Unlike many "nonlinear" regression programs that can only handle a limited set of function forms, NLREG can handle essentially any function whose form you can specify algebraically. NLREG features a full programming language with a syntax similar to C for specifying the function that is to be fitted to the data. This allows you to compute intermediate work variables, use conditionals, and even iterate in loops. With NLREG it is easy to construct piecewise functions that change form over different domains. Since the NLREG language includes arrays, you can even use tabular look-up methods to define the function.