I know this thread has been inactive, but I’ve been learning Julia and having read this thread I thought I would try to convert a frequency estimator from python.

So, here’s a simple algorithm that does pretty well at finding the frequencies.

Note, it forms a big matrix from the input array and takes an SVD, so, maybe start with a subset of the vector first.

```
"""
esprit(x::Array, M::Int, p::Int, Fs::Float64=1.0)
ESPRIT algorithm for frequency estimation.
Estimation of Signal Parameters via Rotational Invariance Techniques
Given length N signal "x" that is the sum of p sinusoids of unknown frequencies,
estimate and return an array of the p frequencies.
# Arguments
- `x::Array`: complex length N signal array
- `M::Int`: size of correlation matrix, must be <= N.
The signal subspace is computed from the SVD of an M x (N-M+1) signal matrix
formed from N-M+1 length-M shifts of the signal x in its columns.
For best performance for 1 sinusoid, use M = (N+1)/3 (according to van der Veen and Leus)
For faster execution (due to smaller SVD), use small M or small N-M
- `p::Int`: number of sinusoids to estimate.
- `Fs::Float64`: sampling frequency, in Hz.
# Returns
length p real array of frequencies in units of Hz.
"""
function esprit(x::Array, M::Int, p::Int, Fs::Float64=1.0)
N = length(x)
X = x[ (1:M) .+ (0:N-M)' ]; # in julia, likely faster to loop than to allocate huge index array
U,s,V = svd(X);
D,_ = eig( U[1:end-1,1:p] \ U[2:end,1:p] );
angle.(D)*Fs/(2*π)
end
```