# Article

**Keywords:**

constrained optimization; convex quadratic function; granular dynamics; Coulomb friction; modified proportioning with gradient projection; Barzilai-Borwein method

**Summary:**

The numerical solution of granular dynamics problems with Coulomb friction leads to the problem of minimizing a convex quadratic function with semidefinite Hessian subject to a separable conical constraints. In this paper, we are interested in the numerical solution of this problem. We suggest a modification of an active-set optimal quadratic programming algorithm. The number of projection steps is decreased by using a projected Barzilai-Borwein method. In the numerical experiment, we compare our algorithm with Accelerated Projected Gradient method and Spectral Projected Gradient method on the solution of a particle dynamics problem with hundreds of spherical bodies and static obstacles.