explain memg(j)=sum([semg(1:(sm-k))' semg(len-sm:(len-sm)+k-1)'])/sm; in matlab

This line of code is performing the calculation of the moving average of semg signal using a window size of sm.

The sum function takes the sum of the element-wise multiplication of two signals which are the concatenation of sm-k elements from the start of semg and k elements from the end of semg.

The apostrophe (') sign in semg(1:(sm-k))' transposes the semg signal. This multiplication by the transpose is equivalent to a dot-product.

The result of this calculation is then divided by the window size sm to get the moving average value of the signal semg.

The final value is stored in the j-th index of the memg signal.

In summary, the code line is applying a moving average filter to the signal semg using a window of size sm and storing the filtered value in the j-th index of another signal memg.