c# sort

Hi, I have a double 2D array: a[0,0]=1.1 a[0,1]=0.1 a[0,2]=2.9 a[0,3]=1.6 a[1,0]=-2.2 a[1,1]=-1.7 a[1,2]=0.3 a[1,3]=-0.4 a[2,0]=2.0 a[2,1]=-0.1 a[2,2]=-1.8 a[2,3]=-3.1 1) I want to sort it in descending order AND save the 2 indexes (in order to know...