subs(): Unexpected simplification behaviour

syms Gr Ra Ri A B Gr1 Gr2 c d
Gr =  2*c*(Ra^2 - Ri^2) - d*(Ra^4 - Ri^4)/2;
Gr1 = subs(Gr, [c*(Ra^2 - Ri^2), -d*(Ra^4 - Ri^4)/2], [A, B])
Gr2 = subs(Gr, [c*(Ra^2 - Ri^2),  d*(Ra^4 - Ri^4)/2], [A, B])

returns

Gr1 =
2*A + B

Gr2 =
2*A - (d*(Ra^4 - Ri^4))/2

Is there a way to convince MATLAB to return

Gr2 = 2*A - B

in the second case without workarounds? Of course, workarounds like

Gr2 = subs(Gr, [c*(Ra^2 - Ri^2), -d*(Ra^4 - Ri^4)/2], [A, -B])

or

Gr1 = subs(Gr, [(Ra^2 - Ri^2),(Ra^4 - Ri^4)], [A/c,-2*B/d])
Gr2 = subs(Gr, [(Ra^2 - Ri^2),(Ra^4 - Ri^4)], [A/c,2*B/d])

will return the desired result, but I have a much more complex expression to substitute and can't work with this subs()-behaviour. I would have expected MATLAB to automatically simplify the respecive equations.

Answer 1

[Philip Caplan]

As you mentioned, "subs" should return "Gr2 = 2*A -B". I have notified the development team here at MathWorks about this behavior and they will hopefully resolve this in a future release.