  This paper presents an efficient 51 lines Matlab code to solve topology
optimization problems. By the fact that the presented code is based on an hard
0-1 optimization method that handles the integer part of the optimization in a
simple fashion and in sub-polynomial time, it has been possible to not only
reduce the number of lines to 51 without sacrificing any readability, but also
to obtain void-solid designs with close to none checkerboard patterns with
improved efficiency. The numerical results in the paper show that the proposed
method has the best average times compared to several codes available in
literature. We also present extensions to different boundary conditions and to
three dimensional designs. The code can be used by students and the newcomers
in topology optimization because of its simplicity and readability. The 51
lines Matlab code and the presented extensions can be downloaded on the webpage
https://github.com/vlatorre847/TOSSE.
