SUPPORTING INFORMATION Effect of step anisotropy on crystal growth inhibition by immobile impurity stoppers

Given the periodicity of our model problem, it suffices to consider a single period cell (the dotted square in Figure 1), which has side length d. The front of the evolving step in this cell can be described by a simple 1D curve in the plane. We first discretize this 1D curve in space with N grid points, (xi, yi), i = 1, 2, . . . , N , which are uniformly spaced with respect to the arc length, s. We initialize our algorithm with a horizontal line from x1 = 0 to xN = d, with yi ≡ 0, ∀i. Because the curve is initially horizontal, the arc length is simply the length of the line.