Chand John


algorithm enabling 20x longer simulations

The National Institutes of Health feature this research


The real world is not perfect. So, if we measure the motion of a person's body as they walk, and measure how hard their feet hit the ground while they walk, those measurements will not be completely consistent: namely, force will not exactly equal mass times acceleration. My colleagues and I developed a new "residual reduction algorithm" that corrects these errors to make force equal mass times acceleration in our measured data. This algorithm has been used by hundreds of users and enabled the generation of an accurate walking simulation 20 times longer than previously feasible.

Over 90 publications have cited the residual reduction algorithm (RRA) as of early 2014.

source code

The residual reduction algorithm (RRA) is distributed as part of the OpenSim source code. The source code for the residual reduction algorithm (RRA) is in this header file and this implementation file.