correlationLags static method

Int32List correlationLags(int in1Len, int in2Len, { CorrOutMode mode = CorrOutMode.full, })

Returns lag indices equivalent to scipy.signal.correlation_lags.

For correlate(in1, in2, mode=...), returned lags align with each output sample in the chosen mode.

Example:

final lags = Conv.correlationLags(4, 3, mode: CorrOutMode.full);
// [-2, -1, 0, 1, 2, 3]

Implementation

static Int32List correlationLags(
  int in1Len,
  int in2Len, {
  CorrOutMode mode = CorrOutMode.full,
}) {
  if (in1Len <= 0 || in2Len <= 0) {
    throw ArgumentError('in1Len and in2Len must be > 0');
  }

  switch (mode) {
    case CorrOutMode.full:
      {
        final start = -(in2Len - 1);
        final len = in1Len + in2Len - 1;
        return Int32List.fromList(
          List<int>.generate(len, (i) => start + i, growable: false),
        );
      }
    case CorrOutMode.valid:
      {
        if (in1Len >= in2Len) {
          final len = in1Len - in2Len + 1;
          return Int32List.fromList(
            List<int>.generate(len, (i) => i, growable: false),
          );
        }
        final len = in2Len - in1Len + 1;
        final start = -(in2Len - in1Len);
        return Int32List.fromList(
          List<int>.generate(len, (i) => start + i, growable: false),
        );
      }
    case CorrOutMode.same:
      {
        final len = in1Len;
        final start = -(in2Len ~/ 2);
        return Int32List.fromList(
          List<int>.generate(len, (i) => start + i, growable: false),
        );
      }
  }
}