If I got this correct, you got 2 files:
%mainfile.m
... some code and variables CA, CH, CV, CD
and
%decompose_kernel.m
function [outputarguments] = decompose_kernel(inputarguments)
... some code
end
If this is correct, I assume you never really worked with functions much before and should read up on how to use them ( https://mathworks.com/help/matlab/ref/function.html ).
So if you want to use the function decompose_kernel in your main file and use the variables CA/CH/CV/CD, you can do it like this:
%mainfile.m
... some code and variables CA, CH, CV, CD
[output] = decompose_kernel(CA, CH, CV, CD);
