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simplifying expressions - Different outputs for Simplify


In at least one instance, the same Simplify command (without using options) produces very different results on two of my computers, one Windows 7 and the other Windows 10. Here is the code:


sf = Simplify;

r1 = (-1 + (-11 - a^2 + 2 a^4) b^2 + (8 - 3 a^2) b^3 + (-2 + a^2) b^4 - 
     b (-6 - 3 a^2 + a Sqrt[b (2 + (-2 + a^2) b)] + 
        2 a^3 Sqrt[b (2 + (-2 + a^2) b)]) - 
     a (Sqrt[b (2 + (-2 + a^2) b)] - 3 Sqrt[b^5 (2 + (-2 + a^2) b)] + Sqrt[

        b^7 (2 + (-2 + a^2) b)]))/(-1 + b - a^2 b + 
     a Sqrt[b (2 + (-2 + a^2) b)])^2;

This is what I got on one of the computers, the Windows 10 one:


Dr1 = D[r1, b] // sf 

(* (6 + 3 a^2 + 2 (-11 - a^2 + 2 a^4) b + 3 (8 - 3 a^2) b^2 + 
    4 (-2 + a^2) b^3 - (a (1 + (-2 + a^2) b))/Sqrt[b (2 + (-2 + a^2) b)] - (
    a b (1 + (-2 + a^2) b))/Sqrt[b (2 + (-2 + a^2) b)] - (
    2 a^3 b (1 + (-2 + a^2) b))/Sqrt[b (2 + (-2 + a^2) b)] - 

    a Sqrt[b (2 + (-2 + a^2) b)] - 2 a^3 Sqrt[b (2 + (-2 + a^2) b)] + (
    a b^6 (-7 - 4 (-2 + a^2) b))/Sqrt[b^7 (2 + (-2 + a^2) b)] + (
    3 a b^4 (5 + 3 (-2 + a^2) b))/Sqrt[b^5 (2 + (-2 + a^2) b)])/(-1 + b - 
    a^2 b + a Sqrt[
     b (2 + (-2 + a^2) b)])^2 - (2 (1 - a^2 + (a - 2 a b + a^3 b)/Sqrt[
      b (2 + (-2 + a^2) b)]) (-1 + (-11 - a^2 + 2 a^4) b^2 + (8 - 
         3 a^2) b^3 + (-2 + a^2) b^4 - 
      b (-6 - 3 a^2 + a Sqrt[b (2 + (-2 + a^2) b)] + 
         2 a^3 Sqrt[b (2 + (-2 + a^2) b)]) - 
      a (Sqrt[b (2 + (-2 + a^2) b)] - 3 Sqrt[b^5 (2 + (-2 + a^2) b)] + Sqrt[

         b^7 (2 + (-2 + a^2) b)])))/(-1 + b - a^2 b + 
    a Sqrt[b (2 + (-2 + a^2) b)])^3 *)

And this, much better expression is what I got on the other computer, the Windows 7 one:


D[r1, b] // sf

(* (2 (-1 + b)^2 b (4 (-2 + 9 a^2 - 8 a^4 + 2 a^6) b^4 - 
     3 a Sqrt[b (2 + (-2 + a^2) b)] - 
     b (-8 - 11 a^2 + 10 a Sqrt[b (2 + (-2 + a^2) b)] + 
        10 a^3 Sqrt[b (2 + (-2 + a^2) b)]) - 

     b^2 (24 - 14 a^2 - 14 a^4 - 29 a Sqrt[b (2 + (-2 + a^2) b)] + 
        14 a^3 Sqrt[b (2 + (-2 + a^2) b)] + 
        4 a^5 Sqrt[b (2 + (-2 + a^2) b)]) - 
     b^3 (-24 + 61 a^2 - 18 a^4 - 4 a^6 + 16 a Sqrt[b (2 + (-2 + a^2) b)] - 
        24 a^3 Sqrt[b (2 + (-2 + a^2) b)] + 
        8 a^5 Sqrt[b (2 + (-2 + a^2) b)])))/(Sqrt[
   b (2 + (-2 + a^2) b)] (-a b + Sqrt[b (2 + (-2 + a^2) b)])^3 (-1 + b - 
     a^2 b + a Sqrt[b (2 + (-2 + a^2) b)])^2) *)

Can I find the reason for this and make it the same on both computers? If so, how to do this? I may have changed global preferences for Simplify on the Windows 7 computer, but don't remember if or how or what I did concerning that. This behavior occurs both in Mathematica 11.2 and Mathematica 11.1.1.





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