ϕ ( t ) = ϕ ¯ + ∑ k = 1 N A k sin ω k t + ∑ k = 1 N B k cos ω k t {\displaystyle \phi (t)={\bar {\phi }}+\sum _{k=1}^{N}A_{k}\sin \omega _{k}t+\sum _{k=1}^{N}B_{k}\cos \omega _{k}t}
To minimize cost function ε 2 {\displaystyle \varepsilon ^{2}}
In discrete space:
at the minimum
in matrix form (7 harmonics). Note: all instances of ∑ {\displaystyle \sum } are actually ∑ i = 1 M {\displaystyle \sum _{i=1}^{M}}