initial step that will be used in downhill simplex algorithm. Roughly said, it determines the spread (size in each dimension) of an initial simplex.

Step, together with initial point (given in cv.DownhillSolver.minimize) are two n-dimensional vectors that are used to determine the shape of initial simplex. Roughly said, initial point determines the position of a simplex (it will become simplex's centroid), while step determines the spread (size in each dimension) of a simplex. To be more precise, if s and x are the initial step and initial point respectively, the vertices of a simplex will be: v_0 := x_0 - (1/2)s and v_i := x_0 + s_i for i=1,2,...,n where s_i denotes projections of the initial step of n-th coordinate (the result of projection is treated to be vector given by s_i := e_i . <e_i . s>, where e_i form canonical basis).