working around #606

no Miller.dispStyle can be either character or enumeration
enforcing variable type is only supported starting with Matlab 2019b
so MTEX should not depend on it
however in the case of MillerConvention it makes the code much easier hence we should take back this commit one we can assume everybody has at least Matlab 2019b

geometry/@Miller/cat.m

@@ -17,7 +17,7 @@
       error('I can not store Miller indices with respect to different crystal symmetries within one list');
     end
 
-    if ms.dispStyle ~= m.dispStyle
+    if MillerConvention(ms.dispStyle) ~= MillerConvention(m.dispStyle)
       warning(['Miller indices are converted to ' char(m.dispStyle)]);
     end
   end

geometry/@Miller/char.m

@@ -12,7 +12,8 @@
 format = get_flag(varargin,{'hkl','hkil','uvw','UVTW'});
 if ~isempty(format), m.dispStyle = format; end
 
-[leftBracket, rightBracket] = m.dispStyle.brackets;
+
+[leftBracket, rightBracket] = brackets(MillerConvention(m.dispStyle));
 
 abc = m.coordinates;
 

geometry/@Miller/cross.m

@@ -13,4 +13,4 @@
 m = cross@vector3d(m1,m2);
 
 % switch from recirprocal to direct and vice verca
-m.dispStyle = -m.dispStyle;
+m.dispStyle = MillerConvention(-MillerConvention(m.dispStyle));

geometry/@Miller/perp.m

@@ -10,6 +10,6 @@
 % Output
 %  n - @Miller
 
-m = Miller(perp@vector3d(m),m.CS,-m.dispStyle);
+m = Miller(perp@vector3d(m),m.CS,MillerConvention(-MillerConvention(m.dispStyle)));
 
 end

geometry/@orientation/round2Miller.m

@@ -45,7 +45,7 @@
   hkl = round(hkl,varargin{:});
 
   uvw = mori \ vector3d.X;
-  uvw.dispStyle = -uvw.dispStyle; % direct lattice
+  uvw.dispStyle = MillerConvention(-MillerConvention(uvw.dispStyle)); % direct lattice
   uvw = round(uvw);
 
   if nargout == 0

plotting/sphericalPlot.m

@@ -315,10 +315,12 @@ function plotLabels(sP,CS,varargin)
         h = Miller(unique(h),CS);
 
         % try direct coordinates
-        h.dispStyle = abs(h.dispStyle);
+        h.dispStyle = MillerConvention(abs(MillerConvention(h.dispStyle)));
 
         % if this gives no integer values - go to reciprocal coordinates
-        if any(angle(round(h),h)>1e-5), h.dispStyle = -h.dispStyle; end
+        if any(angle(round(h),h)>1e-5)
+          h.dispStyle = MillerConvention(-MillerConvention(h.dispStyle)); 
+        end
         h = round(h);
       end