Gradient function not working

I have a 3D grid of data values (F). I modify a series of points (in a 1D strip). When I take the gradient of the function F , the gradient only takes the central difference in one direction. I am unsure why it does not take the difference in 3D?

Here is a simplified version of my code. Any help would be greatly appreciated.

Thanks

%%gradienttest

%test whether gradient works elsewhere

%variables

K = 2.87;   %Thermal conductivity (W/ m K)

%general

sT = 10;  %surface temperature ('C)

Tg = 2;  %Temperature gradient ('C / 100 m)

Ini = 1; %initial conditons

nt = 100; %number of time steps

x = 0:100;
y = 0:100;
z = 0:60;

%%Mesh / grid

[X,Y,Z] = meshgrid(x,y,z);

%%Tnitial temperature model

F = sT + ( (Tg.*K.*Z)./K);Z=Y; 

      x = 101;
      y = 101;
      z = 61;
      for a=1:Ini %Change in temperature of elements
          i=x-45;
          j=y-45;
          %k=z-25;
          k=34:z-22;
          F(j,i,k)=30;
      end
      Tg=gradient(F,100,100,100);

Answer 1

[Stephen23]

According to the gradient documentation:

 [Tx,Ty,Tz] = gradient(...)

[Chris Brown]

Thank you!