How to write script for this

SAP=1/M∑_(i=1)^M▒〖|CWT(ai,n)〗

where i=1,2,3....M
      n=1,2,3...N
      CWT=Continous Wavelet Transfer

[Walter Roberson]

What is the character after the ^M ?

What is the upper limit of summation?

What is being raised to the M'th power?

[Jan]

I assume, this is the LaTeX notation of "sum from i=1 to M".

What is the character behind ^M ? Should there be two | characters to build the norm? If so, which norm?