general series

       ∞
f(x) ~ ∑ cₙ φₙ(x)
      ⁿ⁼⁰

cₙ = ❬͟f͟,φ͟ₙ͟❭͟ᵥ where v is some modulo weighting
      ‖φₙ‖ᵥ²