Minimum Variance

[alexpattyn]

I'll be implementing the minimum variance reconstruction algorithm.

Mozaffarzadeh, Moein, et al. "Linear-array photoacoustic imaging using minimum variance-based delay multiply and sum adaptive beamforming algorithm." Journal of biomedical optics 23.2 (2018): 026002.

[alexpattyn]

Just to give a brief update, I am having some issues with the covariance matrix from python not exactly matching the one from Matlab. I believe this is an issue with an implementation difference between the Hilbert transform from scipy and matlab.

While this is something I'll check before the final commit, I think it should be good enough for now. As the covariance matrix looks the same - just some specific values don't match up.

[jgroehl]

@alexpattyn Will you find the time to open a pull request with your implementation so far? We could take it from there and finalise the code if you like :D Thanks!