diff --git a/zUtil_Cryst/gtCrystFourIndexes2Miller.m b/zUtil_Cryst/gtCrystFourIndexes2Miller.m
index 453b86cd35b1d49d8cec9a2ee753120390dc1e10..6b5c683da02a681f6524c7118621d9a64f5b17c7 100644
--- a/zUtil_Cryst/gtCrystFourIndexes2Miller.m
+++ b/zUtil_Cryst/gtCrystFourIndexes2Miller.m
@@ -4,6 +4,7 @@ function hkl = gtCrystFourIndexes2Miller(hkil, miller_type)
 %
 %     hkl = gtCrystFourIndexes2Miller(hkil, miller_type)
 %     --------------------------------------------------
+%     From 4-index notation to 3-index notation (only hexagonal unit cell)
 %     INPUT:
 %       hkil        = <double>   plane normal Miller-Bravais indexes (Nx4)
 %       miller_type = <string>   'plane' / 'direction'
@@ -18,13 +19,13 @@ function hkl = gtCrystFourIndexes2Miller(hkil, miller_type)
 
 hkl = zeros(size(hkil,1), 3);
 
-switch miller_type
-  case 'direction'
+switch lower(miller_type)
+  case {'direction','dir','d'}
     hkl(:,1) = hkil(:,1) - hkil(:,3);
     hkl(:,2) = hkil(:,2) - hkil(:,3);
     hkl(:,3) = hkil(:,4);
 
-  case 'plane'
+  case {'plane','pl','p'}
     hkl(:,1) = hkil(:,1);
     hkl(:,2) = hkil(:,2);
     hkl(:,3) = hkil(:,4);
diff --git a/zUtil_Cryst/gtCrystMiller2FourIndexes.m b/zUtil_Cryst/gtCrystMiller2FourIndexes.m
index d868165373772ed4d81fe007618b1ccd657a2e39..6d7c2cf31508a208c29a526775b17e48030bfdb5 100644
--- a/zUtil_Cryst/gtCrystMiller2FourIndexes.m
+++ b/zUtil_Cryst/gtCrystMiller2FourIndexes.m
@@ -4,6 +4,7 @@ function [hkil, hkil_int] = gtCrystMiller2FourIndexes(hkl, miller_type)
 %
 %     [hkil, hkil_int] = gtCrystMiller2FourIndexes(hkl, miller_type)
 %     --------------------------------------------------------------
+%     From 3-index notation to 4-index notation (only hexagonal unit cell)
 %     INPUT:
 %       hkl         = <double>   plane normal Miller indexes (Nx3)
 %       miller_type = <string>   'plane' / 'direction'
@@ -21,14 +22,14 @@ function [hkil, hkil_int] = gtCrystMiller2FourIndexes(hkl, miller_type)
 
 hkil = zeros(size(hkl,1), 4);
 
-switch miller_type
-  case 'direction'
+switch lower(miller_type)
+  case {'direction','dir','d'}
     hkil(:,1) = 2*hkl(:,1) - hkl(:,2);
     hkil(:,2) = 2*hkl(:,2) - hkl(:,1);
     hkil(:,3) = - (hkl(:,1) + hkl(:,2));
     hkil(:,4) = 3*hkl(:,3);
 
-  case 'plane'
+  case {'plane','pl','p'}
     hkil(:,1) = hkl(:,1);
     hkil(:,2) = hkl(:,2);
     hkil(:,3) = - (hkl(:,1) + hkl(:,2));
@@ -40,7 +41,7 @@ if nargout > 1
         tmp = hkil(ii,:);
         tmp((tmp > 10^-9 & tmp <= 0.1) | tmp == 0)=[];
         minimum(ii) = max(min(abs(tmp)), 0);
-        hkil_int(ii,:) = hkil(ii,:) ./minimum(ii);
+        hkil_int(ii,:) = hkil(ii,:) ./ minimum(ii);
         hkil_int(ii,:) = fix(hkil_int(ii,:));
     end
 end