You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: cellBoundaryCylindrical3D.m
    path of file: ./repos/FVTool/Boundary
    
    the code of the file until where you have to start completion: function phiBC = cellBoundaryCylindrical3D(phi, BC)
% function phiBC = cellBoundary2D(MeshStructure, BC, phi)
% It creates the matrix of coefficient based on the BC structure provided
% by the user. It also generates the right hand side vector of the linear
% system of equations
%
% SYNOPSIS:
%   phiBC = cellBoundaryCylindrical3D(phi, BC)
%
% PARAMETERS:
%   MeshStructure: a mesh structure created by buildMesh* functions
%   BC: boundary condition structure created by createBC function
%   phi: cell variable created by createCellVariable
%
% RETURNS:

    
function phiBC = cellBoundaryCylindrical3D(phi, BC)
% function phiBC = cellBoundary2D(MeshStructure, BC, phi)
% It creates the matrix of coefficient based on the BC structure provided
% by the user. It also generates the right hand side vector of the linear
% system of equations
%
% SYNOPSIS:
%   phiBC = cellBoundaryCylindrical3D(phi, BC)
%
% PARAMETERS:
%   MeshStructure: a mesh structure created by buildMesh* functions
%   BC: boundary condition structure created by createBC function
%   phi: cell variable created by createCellVariable
%
% RETURNS:
%   phiBC: a cell variable including the values of the ghost cells
%
% EXAMPLE:
%   m = buildMesh2D(3,4,1,1);
%   phi = createCellVariable(m,1);
%   bc = createBC(m);
%   phi_with_ghost = cellBoundary(phi, bc)
%
% SEE ALSO:
%


% extract data from the mesh structure
Nxyz = BC.domain.dims;
Nx = Nxyz(1); Ntetta = Nxyz(2); Nz = Nxyz(3);
dx_1 = BC.domain.cellsize.x(1);
dx_end