Re:Does anyone have an apparent fix for this mathematica problem?
- To: mathgroup at yoda.ncsa.uiuc.edu
- Subject: Re:Does anyone have an apparent fix for this mathematica problem?
- From: uunet!mathnx.byu.edu!smithw (William V. Smith)
- Date: Thu, 7 Jun 90 22:16:39 MDT
Yes. There is a fix. It is available from your local friendly NeXT
Rep. Here's what happens with the fix:
In[1]:= InputForm[(b*c*(a + d - (a^2 + 4*b*c - 2*a*d + d^2)^(1/2))^3)/
(4*(a - d + (a^2 + 4*b*c - 2*a*d + d^2)^(1/2))*
(a^2 + 4*b*c - 2*a*d + d^2)^(1/2)) -
(b*c*(a + d + (a^2 + 4*b*c - 2*a*d + d^2)^(1/2))^
3)/
(4*(a - d - (a^2 + 4*b*c - 2*a*d + d^2)^(1/2))
*
(a^2 + 4*b *c - 2*a*d + d^2)^(1/2))]
Out[1]//InputForm=
(b*c*(a + d - (a^2 + 4*b*c - 2*a*d + d^2)^(1/2))^3)/
(4*(a^2 + 4*b*c - 2*a*d + d^2)^(1/2)*
(a - d + (a^2 + 4*b*c - 2*a*d + d^2)^(1/2))) -
(b*c*(a + d + (a^2 + 4*b*c - 2*a*d + d^2)^(1/2))^3)/
(4*(a^2 + 4*b*c - 2*a*d + d^2)^(1/2)*
(a - d - (a^2 + 4*b*c - 2*a*d + d^2)^(1/2)))
In[2]:= rule={a->1,b->2,c->3,d->4}
Out[2]= {a -> 1, b -> 2, c -> 3, d -> 4}
In[3]:= N[res//.rule]
Out[3]= res
In[4]:= res=%1;
In[5]:= N[res//.rule]
Out[5]= 37.
In[6]:= N[Together[Expand[res]]//.rule]
Out[6]= 37.
In[7]:= N[Simplify[res]//.rule]
Out[7]= 37.
The bad result was from a known bug in the Together function
which is called by Simplify so both gave the wrong answer.