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Re: very odd failure of Solve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg131654] Re: very odd failure of Solve
  • From: Richard Fateman <fateman at cs.berkeley.edu>
  • Date: Mon, 16 Sep 2013 05:15:47 -0400 (EDT)
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  • References: <l1446c$psj$1@smc.vnet.net>

On 9/15/2013 4:03 AM, Alan wrote:
> Setting an irrelevant parameter to 0 baffles Solve. Why?
> Thanks,
> Alan Isaac
>
> $Assumptions =.
> ClearAll[f1]
> f1[x_] := s*x^\[Alpha] - (a + b + c)*x
> Solve[f1[x] == 0, x]  (* Solve works *)
> Solve[(f1[x] /. {b -> 0}) == 0, x]  (* Solve fails *)
<snip>

Running Reduce[ {%==0}, {x} ] on either equation seems to go into
an infinite loop.  That maybe be an independent bug, though.

I expected that somehow fiddling with the variable names would
do something, and that the ordering of a,b,c, alpha was critical.
Out of curiosity I tried a few variants to generate a better
hypothesis, but ran out of, um, curiosity.





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