  The squeezing process of a three-dimensional quantum system by use of an
external deformed one-body oscillator potential can also be described by the
$d$-method, without external field and where the dimension can take non-integer
values. In this work we first generalize both methods to $N$ particles and any
transition between dimensions below $3$. Once this is done, the use of harmonic
oscillator interactions between the particles allows complete analytic
solutions of both methods, and a direct comparison between them is possible.
Assuming that both methods describe the same process, leading to the same
ground state energy and wave function, an analytic equivalence between the
methods arises. The equivalence between both methods and the validity of the
derived analytic relation between them is first tested for two identical bosons
and for squeezing transitions from 3 to 2 and 1 dimensions, as well as from 2
to 1 dimension. We also investigate the symmetric squeezing from 3 to 1
dimensions of a system made of three identical bosons. We have in all the cases
found that the derived analytic relations between the two methods work very
well. This fact permits to relate both methods also for large squeezing
scenarios, where the brute force numerical calculation with the external field
is too much demanding from the numerical point of view, especially for systems
with more than two particles.
