Hi Matthew,
I observed the same issue with 'rewrite' and 'unitConvert' (https://www.mathworks.com/help/symbolic/unitconvert.html). Here is a workaround you can use:
You can define a new units system in MATLAB using the function 'newUnitSystem'
Refer to the following code:
u = symunit;
% Modify the SI units to use Astrounit for length, Yr for time and Solar
% for mass
SIUnits = baseUnits('SI'); % Extract the Base Units
newUnits = subs(SIUnits,[u.m u.s u.kg],[Unit1 Unit2 Unit3]); % Substitute the desired units
% Define the new unit system SI_myUnits using the new base units
newUnitSystem('SI_myUnits',newUnits);
% Rewrite G using the new Unit System
G=6.6743E-11*u.m^3*u.kg^(-1)*u.s^(-2);
G_2=rewrite(G,'SI_myUnits');
The answer will be in terms of your defined units only:
G_2 =
(131406052046712958830620234047406505291/3328529041768042103396741079787110400)*([Astrounit]^3/([Solar]*[Yr]^2))
You may also use 'findUnits' to verify the units of 'G_2' :
findUnits(G_2)
ans =
[[Astrounit], [Solar], [Yr]]
This will resolve the issue and it works for all powers greater than or equal to 3.
