Slider Proposal is Symmetric

The upper rectangle shows the forward proposal window, while the lower rectangle shows the reverse proposal window. Dragging the mouse above the axis changes the value of θ (the current parameter value). Dragging the mouse below the axis changes the value of θ* (the proposed parameter value). If θ* lies in the dark purple zone, then that value could have arisen either because it was proposed directly or it was reflected to that spot after a point to the left of zero was proposed. Note that if the forward proposal results in a value of θ* in the dark purple zone, then the reverse proposal results in a value of θ in a dark purple zone, and if the forward proposal results in a value of θ* in the lavender zone, then the reverse proposal results in a value of θ in the lavender zone. Thus, the proposal is symmetric and the Hastings ratio equals 1.