Hotfix: Prevent div-by-zero in dynamic ratio colorbar range

gcpy/plot/six_plot.py
- In routine "compute_vmin_vmax_for_ratio_plots":
  - If vmin is nonzero, compute vmax = 1.0 / vmin
  - If vmin is zero, then
    - Set vmax = np.abs(np.nanmax(plot_val)
    - Set vmin = 1.0 / vmax
  - Values will be swapped (as before) if vmin > vmax

This fix is necessary in order potential div-by-zero errors in
the computation of the dynamic ratio colorbar limits vmin & vmax.

Signed-off-by: Bob Yantosca <[email protected]>

gcpy/plot/six_plot.py

@@ -547,9 +547,13 @@ def vmin_vmax_for_ratio_plots(
         vmin = np.min(
             [np.abs(np.nanmin(plot_val)), np.abs(np.nanmax(plot_val))]
         )
-        vmax = 1.0 / vmin
+        if np.abs(vmin) > 0.0:                     # If vmin > 0, compute
+            vmax = 1.0 / vmin                      # vmax as its reciprocal
+        else:
+            vmax = np.abs(np.nanmax(plot_val))     # Otherwise compute vmin
+            vmin = 1.0 / vmax                      # as reciprocal of vmax
         if vmin > vmax:
-            vmin, vmax = vmax, vmin
+            vmin, vmax = vmax, vmin                # Swap values if needed
         verbose_print(verbose, rowcol, vmin, vmax)
         return vmin, vmax