Given a cam_to_sRGB matrix, how do I generate ForwardMatrix?

I have a matrix that will convert my raw camera RGB data to sRGB space, for example when I apply the matrix to the white balance corrected raw data in MATLAB, I get a good looking output image.

I want to create a DNG file from this raw data, but I can't figure out how to generate the ForwardMatrix. For that matter, I'm not even sure whether it is the ForwardMatrix I should be generating or the ColorMatrix (or both?).

To simplify things let's assume the cam_to_sRGB matrix I have is for the A illuminant and the image was captured under that same illuminant. (I can extrapolate later for high color temperature matrix.)

What exact steps must I take to generate the ForwardMatrix1 given the cam_to_sRGB matrix that I have? What should the ColorMatrix1 be in this case? (identity?)

Specific example:

cam_to_sRGB =

What would the ForwardMatrix1 be? What would the ColorMatrix1 be?

I found the DNG spec not helpful. It tells me how to generate an image given already existing DNG matrixes. I need to know how to generate those matrixes in the first place.

Thanks,

Ken