Time Series Synchronization (not working, I don't know why)

tss.js

// Source: http://lexfridman.com/fast-cross-correlation-and-time-series-synchronization-in-python/
// Using: https://github.com/nicolaspanel/numjs
function cross_correlation_using_fft (x, y) {
  let f1 = nj.fft(x)
  let f2 = nj.fft(nj.flip(y, 1))
  let cc = nj.ifft(f1.multiply(f2)).slice(0, [0, 1])
  return fftshift(cc)
}

// shift < 0 means that y starts 'shift' time steps before x
// shift > 0 means that y starts 'shift' time steps after x
function compute_shift (x, y) {
  console.assert(x.shape[0] === y.shape[0], x.shape[0] + ' !== ' + y.shape[0])
  const c = cross_correlation_using_fft(x, y)
  console.assert(c.shape[0] === x.shape[0], c.shape[0] + ' !== ' + x.shape[0])
  const zero_index = Math.floor(x.shape[0] / 2) - 1
  const shift = zero_index - c.tolist().indexOf(c.max())
  return shift
}

// fftshift from https://github.com/oramics/fftshift/blob/master/index.js
function rotate (src, n) {
  var len = src.length
  reverse(src, 0, len)
  reverse(src, 0, n)
  reverse(src, n, len)
  return src
}

function reverse (src, from, to) {
  --from
  while (++from < --to) {
    var tmp = src[from]
    src[from] = src[to]
    src[to] = tmp
  }
}

function fftshift (src) {
  // Convert ndArray to Array then back to ndArray again
  const arr = src.tolist()
  const len = arr.length
  return nj.array(rotate(src, Math.floor(len / 2))).reshape(src.shape)
}

// Test function
compute_shift(
  nj.concatenate(nj.arange(10).reshape(10, 1), nj.arange(100, 110, 1).reshape(10, 1)),
  nj.concatenate(nj.arange(10).reshape(10, 1), nj.arange(200, 210, 1).reshape(10, 1))
)

// Expected: 100
// Returns: 5