polyparci

POLYPARCI calculates confidence intervals for parameters estimated by ‘polyfit’.

POLYPARCI uses the procedures outlined in the ‘polyfit’ documentation to calculate the covariance matrix, and uses ‘betainc’ and ‘fzero’ to calculate the cumulative t-distribution and the inverse t-distribution for a given probability and degrees-of-freedom. It uses only core MATLAB functions and does not require the Statistics Toolbox.
The t-distribution and t-statistic calculations have a relative error of about 1E-012 compared to the Statistics Toolbox functions ‘tcdf’ and ‘tinv’. The relative error of the confidence intervals is about 1E-005 compared to those calculated by ‘nlinfit’ and ‘nlparci’ with the same model on the same data.