I am dealing with a cosmological parameter estimation problem. I have a sum of squares function (chi-squared) of two parameters and I have minimized it using fminsearch, to find the best fit. Now, I want to plot 1-sigma, 2-sigma confidence contours for this. My parameter probability distribution may not be Gaussian. So , I don't want to do it in the usual way of adding 2.3 to chi-squared minimum and drawing the contour for 1-sigma. How can I draw a contour that encloses 68% of the area of the surface?