There is a problem when I'm reading a paper.
Equation:
$min_p|p-p^*|^2+\alpha |R(p)|^2 + \beta |D(p)-\delta|^2$,
where $p, p^*, R(p), D(p), \delta$ are all $M\times N$ matrices, and $p^*, R(), D(), \delta$ are known.
The paper just mentioned "which (this equation) represents a sparse quadratic in $p$". According to this sentence, I cannot figure out how to solve this equation. Any hints would be appreciated.
Here is the paper. The equation is on Page 4, eq.6.