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MathGroup Archive 1995

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Re: Bugs with transcendental functions?

  • To: mathgroup at
  • Subject: [mg1796] Re: Bugs with transcendental functions?
  • From: wjrowe at (Bill Rowe)
  • Date: Mon, 31 Jul 1995 23:06:39 -0400
  • Organization: Hughes Space Company

In article <DC7E1v.1s9 at>, jin at (gum) wrote:

|I have two similar equations listed below. The 1st one 
|came out OK, but the 2nd one didn't go anywhere.
|The only difference is "p" in the 1st one is replaced
|by "a" in the 2nd one.
|I'm using mathematica 2.0 on NeXTStep 3.0.  Is it a
|bug of the version of MMA I have? 
|1. Input:=
|          Solve[p (-Log[x + a z]+ Log[ w + a z])/qq== y, x]
|                 w + a z
|{{x -> -(a z) + ---------}}
|                 (qq y)/p
|                E
|2. Input:=
|           Solve[a (-Log[x + a z]+ Log[ w + a z])/qq== y, x]
|   The equations appear to involve transcendental
|     functions of the variables in an essentially
|     non-algebraic way.
|      a (Log[w + a z] - Log[x + a z])
|Solve[------------------------------- == y, x]
|                    qq

I am sure it is not a bug related to your version of MMA since I get the
same result using MMA version 2.2.1 on a Macintosh.

In your first example none of the variables which appear as arguments to
the Log function appear outside of the Log function. Consequently, a
simple inversion of the Log function solves the equation.

In you second example, the symbol 'a' appears as an argument to the Log
function as well as elsewhere in the equation. I believe the Solve
function assumes the symbol 'a' could be a function of x, hence the

Basically the behavior you describe is not a bug but a result of the
design of the Solve function.

#include std disclaimers

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