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|    sci.math.symbolic    |    Symbolic algebra discussion    |    10,432 messages    |
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|    Message 10,331 of 10,432    |
|    Sam Blake to All    |
|    A rational integral in Rubi    |
|    10 Oct 23 21:06:00    |
      From: samuel.thomas.blake@gmail.com              I was pleased to see the following concise result from Rubi              In[8203]:= Int[(2 u + u^2)/(2 + 4 u + 2 u^2 + u^4), u]       Out[8203]= ArcTan[u^2/(Sqrt[2] (1 + u))]/Sqrt[2]              My implementation of Bronstein's Risch algorithm (from Symbolic Integration I)       returns two arctangents              In[8206]:= Risch[(2 u + u^2)/(2 + 4 u + 2 u^2 + u^4), u]       Out[8206]= (ArcTan[(-1 + u)/Sqrt[2]] - ArcTan[(2 + 2 u + (-1 + u)       u^2)/Sqrt[2]])/Sqrt[2]              and Mathematica returns the naive form              In[8207]:= Integrate[(2 u + u^2)/(2 + 4 u + 2 u^2 + u^4), u]       Out[8207]= 1/4 RootSum[        2 + 4 #1 + 2 #1^2 + #1^4 &, (2 Log[u - #1] #1 + Log[u - #1] #1^2)/(        1 + #1 + #1^3) &]              FriCAS also returns two arctangents              (8) -> integrate((2*u + u^2)/(2 + 4*u + 2*u^2 + u^4), u)               +-+ 3 2        (u - 1)\|2 u - u + 2 u + 2        atan(-----------) - atan(-----------------)        2 +-+        \|2        (8) -------------------------------------------        +-+        \|2        Type: Union(Expression(Integer),...)              Perhaps there is still some room for improvement in the log to arctan       conversions in symbolic integrators...              Sam              --- SoupGate-Win32 v1.05        * Origin: you cannot sedate... all the things you hate (1:229/2)    |
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