Why is my code returning the error "Index in position 1 exceeds array bounds" when calling adjacent()?

I have the following snippet of code that yields the error "Index in position 1 exceeds array bounds" when calling the function adjacent():

function out = polycubes()
% Yields array of polycubes of orders 1-10 which fit within a 3x3x3 cube
% Input: none
% Output: array of all polycubes of orders 1-10 which fit within a 3x3x3
% cube
pCubes = zeros(403006,3,3,3);

% Initializes start cube
pCubes(1,:,:,1) = zeros(3,3);
pCubes(1,:,:,2) = [0 0 0; 0 1 0; 0 0 0];
pCubes(1,:,:,3) = zeros(3,3);

% Starts master counter
pCubeIndex = 1;

while true
    % Checks if polycube contains 10 cubes. If not, moves to next polycube
    % to be built upon
    if sum(pCubes(pCubeIndex,:,:,:),"all") == 10
        pCubeIndex = pCubeIndex + 1;
        if mod(pCubeIndex,1000) == 0
            disp("Cube ", pCubeIndex, ": ", pCubes(pCubeIndex));
        end
    % Breaks if no polycubes less than order 10 remain to be built upon
    elseif sum(pCubes(pCubeIndex,:,:,:),"all") == 0
        if mod(pCubeIndex,1000) == 0
            disp("Cube ", pCubeIndex, ": ", pCubes(pCubeIndex));
        end
        break
    else
        % Creates list of cells adjacent to existing cubes in a polycube
        adjCells = zeros(26,3);
        counter = 0;
        for a = 1:3
            for b = 1:3
                for c = 1:3
                    if a ~= 2 | b ~= 2 | c ~= 2
                        if pCubes(pCubeIndex,a,b,c) == 0
                            if adjacent(pCubes(1,:,:,:),a,b,c) % error here
                                adjCells(counter,:) = [a b c];
                                counter = counter + 1;
                            end
                        end
                    end
                end
            end
        end
    end
end

Here is the entire code for adjacent():

function out = adjacent(cube,x,y,z)
    output = false;
    if x + 1 <= 3 
        if cube(x+1,y,z) ~= 0
            output = true;
        end
    end
    if x - 1 >= 1 
        if cube(x-1,y,z) ~= 0
            output = true;
        end
    end
    if y + 1 <= 3 
        if cube(x,y+1,z) ~= 0
            output = true;
        end
    end
    if y - 1 >= 1 
        if cube(x,y-1,z) ~= 0
            output = true;
        end
    end
    if z + 1 <= 3 
        if cube(x,y,z+1) ~= 0
            output = true;
        end
    end
    if z - 1 >= 1 
        if cube(x,y,z-1) ~= 0
            output = true;
        end
    end
    out = output;

Answer 1

[Walter Roberson]

                            if adjacent(pCubes(1,:,:,:),a,b,c) % error here

You are passing in a 1 x something x something by something array

        if cube(x+1,y,z) ~= 0

You are addressing it as a something by something by something array, forgetting that the leading dimension of it is 1

[Ian]

I see the error. pCubes is a 403006 x 3 x 3 x 3 array; I'd like to take off the first "slice," the 3x3x3 cube of (1,:,:,:). Is there quick way to convert an element of a 4D array into a 3D array?

[Stephen23]

If you want to write fragile code: https://www.mathworks.com/help/matlab/ref/squeeze.html

If you want to write robust code: https://www.mathworks.com/help/matlab/ref/double.permute.html

[Walter Roberson]

You should also consider moving the 403006 to the last dimension; it will be more efficient.