This program will try to find the fit to the match function about some template. It is called with four arguments: the mass of body 1 (in solar masses), the mass of body 2 (in solar masses), the value of the match for which it tries to fit, and (twice) the order of the post-Newtonian expansion used to compute the templates. For example, match_fit 1.2 1.8 .98 4 will try to find a fit to the .98 match contour near the template for the using post-2-Newtonian templates.
The program first attempts to find a parabolic fit; if it is unable to do so, it then tries a cubic. If the cubic fails, you are in a region of parameter space where the match is badly behaved. This is typically the case if you ask for masses that are too large--for example, no fit can be found near a solar mass binary with the LIGO 40-meter prototype noise curve. When the masses are large, the system radiates very few gravitational-wave cycles in the instrument's frequency band; and, those cycles typically correspond to a strongly relativistic regime of inspiral. If you find yourself in this circumstance, either give up on the large mass binaries, or try to find a fit at a match level closer to 1.