protected void range(int stride) {
		int i;
		if (length >= stride) {
			dxmax = data[0];
			dymax = data[1];
			dxmin = dxmax;
			dymin = dymax;
		}
		else {
			dxmin = 0.0;
			dxmax = 0.0;
			dymin = 0.0;
			dymax = 0.0;
		}

		for (i = stride; i < length; i += stride) {
			if (dxmax < data[i]) {
				dxmax = data[i];
			}
			else if (dxmin > data[i]) {
				dxmin = data[i];
			}
			if (dymax < data[i + 1]) {
				dymax = data[i + 1];
			}
			else if (dymin > data[i + 1]) {
				dymin = data[i + 1];
			}
		}

		if (xaxis == null) {
			xmin = dxmin;
			xmax = dxmax;
		}
		if (yaxis == null) {
			ymin = dymin;
			ymax = dymax;
		}
	}