https://en.wikipedia.org/wiki/Buckingham_%CF%80_theorem In engineering, applied mathematics, and physics, the
Buckingham π theorem is a key
theorem in
dimensional analysis. It is a formalization of
Rayleigh's method of dimensional analysis. Loosely, the theorem states that if there is a physically meaningful equation involving a certain number
n of physical variables, then the original equation can be rewritten in terms of a set of
p =
n−
k dimensionless parameters π
1, π
2, ..., π
p constructed from the original variables. (Here
k is the number of physical dimensions involved; it is obtained as the
rank of a particular
matrix.)
The theorem provides a method for computing sets of dimensionless parameters from the given variables, or
nondimensionalization, even if the form of the equation is still unknown.
More formally, the number of dimensionless terms that can be formed,
p, is equal to the
nullity of the
dimensional matrix, and
k is the
rank. For experimental purposes, different systems that share the same description in terms of these
dimensionless numbers are equivalent.
In mathematical terms, if we have a physically meaningful equation such as
{\displaystyle f(q_{1},q_{2},\ldots ,q_{n})=0,}
where the
qi are the
n physical variables, and they are expressed in terms of
k independent physical units, then the above equation can be restated as
{\displaystyle F(\pi _{1},\pi _{2},\ldots ,\pi _{p})=0,}
where the π
i are dimensionless parameters constructed from the
qi by
p =
n −
k dimensionless equations — the so-called
Pi groups — of the form
{\displaystyle \pi _{i}=q_{1}^{a_{1}}\,q_{2}^{a_{2}}\cdots q_{n}^{a_{n}},}
where the exponents
ai are rational numbers (they can always be taken to be integers by redefining π
i as being raised to a power that clears all denominators).