Unstable examples of the tests using scheme #2 with time steps beyond the stability limit. Top left shows the temperature evolution in the one-dimensional test with dt = 200dt_TC. Top right presents a temperature colormap for the static ring problem using dt = 33dt_TC and t = 100. The bottom left panel shows a temperature colormap of the temperature for the hotplate test, using a time step dt = 500dt_tc. Bottom right panel shows a contour of temperature in the three-dimensional static ring problem in an early stage, t = 5 s, using a time step dt = 45dt_tc.