If you want to do a linear regression and you have the Statistics Toolbox, my choice would be the regress function. If you ask it, you can get the regression coefficients and their confidence intervals, and the confidence intervals on the fit, as well as other statistics. All that information is in the documentation, so I won’t repeat it here.
If you want to stay with polyfit and polyval, asking polyval for ‘delta’ produces what appear from the documentation as standard errors of the estimate for various estimated values of y. You can calculate the 95% confidence intervals using the inverse t-statistic with n-2 degrees of freedom, n being the number of data pairs. Multiply each ‘delta’ by the same t-score.
If you want the 95% confidence limits on the parameter estimates calculated by polyfit, the File Exchange function polyparci can provide them.
