ACES NPM round about calculation question

[eyeforcolor]

Reading through the google colab explanation of "how to derive the primaries and white point from an ACES Input Device Transform (IDT) matrix" I see the following code to calculate the NPM

NPM = matrix_RGB_to_RGB_to_normalised_primary_matrix( np.linalg.inv(M_IDT), colour.RGB_COLOURSPACES['ACES2065-1'].matrix_XYZ_to_RGB)

Wouldn't you get similar matrix by doing the below?
NPM = np.dot(colour.RGB_COLOURSPACES['ACES2065-1'].matrix_RGB_to_XYZ, M_IDT)

I checked the output and they do give exact same result, just wanted to understand if there is something I am missing when using the method from google colab.

Please let me know!

[KelSolaar]

Hello @eyeforcolor,

I don't have the document front of me so I'm not sure what the matrix_RGB_to_RGB_to_normalised_primary_matrix definition does, it is not a colour definition.

Maybe @aforsythe or @sdyer can help here!

Cheers,

Thomas

[nick-shaw]

Don't know about a colab, but there is a RGB_to_RGB_matrix_to_normalised_primary_matrix() function defined in this post.

@KelSolaar, you may want to fix whatever has gone wrong with the equation formatting in that post.