# GROMACS 2020.6 release notes¶

This version was released on March 4th, 2021. These release notes document the changes that have taken place in GROMACS since the previous 2020.5 version, to fix known issues.

## Fixes where mdrun could behave incorrectly¶

### Cosine acceleration failed to abort if it could not be run¶

Cosine acceleration is only compatible with the leap-frog integrator (integrator = md). GROMACS did, however, accept input files requesting cosine acceleration for other integration algorithms, and did report viscosity-related quantities from these simulations. Since the cosine acceleration was never applied in these cases, any results obtained from simulations with enabled cosine acceleration and integrators other than md should be regarded as invalid.

Issue 3903

## Fixes for gmx tools¶

### Fix range checking bug in gmx covar¶

A check was inverted causing range checking to be applied wrong.

Issue 3902