Improve 3D-plot section

Signed-off-by: Aaron Erhardt <aaron.erhardt@t-online.de>

Matlab/Matlab.md

@@ -528,13 +528,32 @@ handle.Children(1).LineWidth = 2; % get line from handle and change width
 plot3(x, y, z);
 ```
 
-### Meshgrid
+### Surfaces
+
+Generate grid
+
+```matlab
+% Generate grid from matrices with duplicate rows of x and duplicate columns of y
+[X Y] = meshgrid(x, y); % Matrices with dimension length(x) x length(y)
+mesh(X, Y)              % Plot mesh
+
+Z = X.^2 - Y            % use (uppercase!) X and Y to calculate Z
+mesh(X, Y, Z)           % Plot mesh with Z coordinate
+```
+
+Mesh surface plot
+
+```matlab
+mesh(X, Y)              % Plot mesh (using X and Y from meshgrid)
+
+Z = X.^2 - Y            % use (uppercase!) X and Y to calculate Z
+mesh(X, Y, Z)           % Plot mesh with Z coordinate
+```
+
+Surface plot
 
 ```matlab
-% Grids are simply specified by matrices of coordinates
-[X Y] = meshgrid(x, y, z); % Generate grid
-mesh(X, Y)                 % Plot mesh
-mesh(X, Y, Z)              % Plot mesh with Z coordinate
+surf(X, Y, Z)           % Similar to mesh but always with Z coordinate
 ```
 
 # Functions