Summary of wavelets

https://en.wikipedia.org/wiki/Wavelet_transform

https://en.wikipedia.org/wiki/Discrete_wavelet_transform

Read the 2nd URL link... "One level of the transform" (i.e. a single level of the filterbank)

"Due to the decomposition process the input signal must be a multiple of 2^n where n is the number of levels."  


Then read the Haar Wavelet java source...

```

public static int[] discreteHaarWaveletTransform(int[] input) {
    // This function assumes that input.length=2^n, n>1
    int[] output = new int[input.length];

    for (int length = input.length / 2; ; length = length / 2) {
        // length is the current length of the working area of the output array.
        // length starts at half of the array size and every iteration is halved until it is 1.
        for (int i = 0; i < length; ++i) {
            int sum = input[i * 2] + input[i * 2 + 1];
            int difference = input[i * 2] - input[i * 2 + 1];
            output[i] = sum;
            output[length + i] = difference;
        }
        if (length == 1) {
            return output;
        }

        //Swap arrays to do next iteration
        System.arraycopy(output, 0, input, 0, length);
    }
}

```

You'll realise, that the DWT requires "N" levels (filterbanks) ... where the input (number of samples) is 2^N...

NB: The inner loop that calculates the sum and difference is particular for the "Haar Wavelet".

Depending on the mother wavelet chosen, this may be different equation/formula/algorithm.

That's all!