vp-comparefit issue, due to arclength errors

Created by: comane

@Zaharid , @enocera Issue with vp-comparefit due to arclength function. my guess is that the problem arises from these lines of the code within validphys.arclength.plot_arc_lengths: yvalues = arclengths.stats.central_value() ylower, yupper = arclengths.stats.errorbar68() ylower = yvalues - ylower yupper = yupper - yvalues Some of the replicas might be shorter than the central replica. The problem is thus probably fixed by taking the absolute value of the difference.

Another possible issue might be in validphys.arclength.arc_lengths, namely, in res += integrate.simps(1 + np.square(fdiff), ixgrid[1][1:]) It looks like a square root is missing here: res += integrate.simps(np.sqrt(1 + np.square(fdiff)), ixgrid[1][1:])