torontoanalyst

Forget about the sign. The sign is part of the expression. We are not talking about “Delta S” but “minus delta S”
hence if you just need to plug the figure if your given the repurchase yield
Read again your quote from Grinold: “the second term - delta S… Equals the repurchase yield”. The sign is included in the term!!!
And what are you given? The repruchase yield! Wow..
no need to touch the sign in the final equation!