We assume that the Fourier transform is merely an optional mathematical tool that can be dispensed with.
The statistical theory of Cairo techniques predicts the general solution of a time-dependent PDE as follows:
f(x,y,z,t)=D(N).(b+S) + B^N.IC..(1)
where D(N) is the transfer function = B+B^2+B^3 +...+B^N
b is the vector of 1D, 2D, and 3D boundary conditions, arranged in the appropriate order.
IC is the vector of initial conditions.
B is the well-defined transition matrix for the considered closed control volume.
One of the drawbacks of the mathematical Fourier transform is that it predicts the solution for 1D, in the x domain GT -∞ and LT ∞, and is not defined for the domain of the x elements of [a,b]. The Fourier transform itself predicts the wave solution for 1D, over the entire range -∞