Equation (1) can be discretized on a rectangular grid with (S 9 F) size-and-shape values (s i , f r,j ) comprising all combinations of S equidistant sedimentation coefficient values from s 1 = s min to s S = s max (with constant mesh size Ds ¼ ðs S À s 1 Þ=ðS À 1Þ ¼ s iþ1 À s i ), and F frictional ratio values from f r,1 = f r,min to f r,F = f r,max (with constant mesh size Df r ¼ ðf r;F À f r;1 Þ=ðF À 1Þ ¼ f r;jþ1 À f r;j ). With the data being (N 9 M) discrete signal values at radius r n and time t m , abbreviated as a nm , (1) leads to the linear leastsquares problem Min c i;j !0 X n;m a nm À X S i¼1 X F j¼1 c i;j vðs i ; f r;j ; r n ; t m ÞÀbðr n ÞÀbðt m Þ