Matrix Gradient calculation of Norm 2 expression

Hi,

I'm trying to get an analytic solution to the following problem

d/dH(||Y-H*X||^2)

Y,X - are matrixes of the same size H - a much smaller matrix * - stands for 2D convolution operator - stand for Norm 2 operation

The result should be a gradient in the dimentions of H.

Thanks