Setting a limit in an array

I am trying to set a limit for values within an array between a set of point. I have a 3D array - say 100x100x100.

I want to set a limit of 30, so if the values are lower they become 30. I also only want to apply the values between 40 and 50 in the z axis... I have tried a few methods, but can't seem to get it to work. Any help would be appreciated.

This is what I have tried so far..

     for a=1:Ini
         x=100;
         y=100;
         z=100;
         i=2:x-1;
         j=2:y-1;
         k=40:z-50;
     F(F(j,i,k)<30)=F(F(j,i,k)<30)./F(F(j,i,k)<30)+30;
     end

and separately -

     for a=1:Ini
         x=100;
         y=100;
         z=100;
         i=2:x-1;
         j=2:y-1;
         k=40:z-50;
     idx=find(F(j,i,k)<30);
     idx=(idx.*0)+30;
     [i,j,k]=ind2sub(size(F),idx);
end

[Jan]

I do not understand "apply the values between 40 and 50 in the z axis". Where does this point appear in the code? What is Ini? Why do you look at 2:x-1 only and not at the margins?

[Chris Brown]

Sorry that wasn't clear. 40 and 50 referring to the z dimension - see k within the loop. Ini is number of iterations - this is part of a bigger loop, where each step I want to limit the data to 30 minimum.

Answer 1

[Alexandra Harkai]

Given initial matrix F, this will floor entries at 30 in between z 'axis' (from and including) 40 and 50:

F(:,:,40:50) = max( 30, F(:,:,40:50) );