#2743 solve does not correctly solve

None
closed
nobody
solve (14)
5
2014-06-05
2014-06-02
No

solve([9.25=sqrt(2*h/10)+h/340],[h]);
returns [h=−(340*sqrt(h)−629*5^(3/2))/sqrt(5)]
Notice sqrt(h) in the right side .
wolframalpha returns h = -85 (4 sqrt(1785)-173) ~~ 340.25


wxMaxima version: 13.4.0
Maxima version: 5.33.0
Maxima build date: 2014-05-16 22:05:41
Host type: i686-pc-linux-gnu
Lisp implementation type: GNU Common Lisp (GCL)
Lisp implementation version: GCL 2.6.10


Discussion

  • Robert Dodier

    Robert Dodier - 2014-06-05
    • labels: --> solve
    • Description has changed:

    Diff:

    --- old
    +++ new
    @@ -1,7 +1,7 @@
    -solve([9.25=sqrt(2*h/10)+h/340],[h]); 
    -returns [h=−(340*sqrt(h)−629*5^(3/2))/sqrt(5)] 
    +`solve([9.25=sqrt(2*h/10)+h/340],[h]);`
    +returns `[h=−(340*sqrt(h)−629*5^(3/2))/sqrt(5)]` 
     Notice sqrt(h) in the right side .
    -wolframalpha returns h = -85 (4 sqrt(1785)-173) ~~ 340.25
    +wolframalpha returns `h = -85 (4 sqrt(1785)-173)` ~~ 340.25
     -------------------------------------------------------------
     wxMaxima version: 13.4.0
     Maxima version: 5.33.0
    
    • status: open --> closed
     
  • Robert Dodier

    Robert Dodier - 2014-06-05

    I agree that the return value of solve is less useful in this case. It is valid, in a sense -- if you solve the equation h = ... sqrt(h) ... by some means (e.g., numerically via find_root) you'll get the answer.

    In this case, to_poly_solve can find the result while solve cannot. I agree that this is a needless difficulty for users. Anyway here it is:

    (%i1) load (to_poly_solve) $
    (%i2) to_poly_solve ([9.25 = sqrt(2*h/10) + h/340], [h]);
                                                 3/2           3/2
    (%o2)         %union([h = 14705 - 4 sqrt(3) 5    sqrt(7) 17   ])
    (%i3) float (%);
    (%o3)                   %union([h = 340.2514814912247])
    

    I'm going to close this report since there is not an identifiable bug in solve here. It is well understand by the developers that solve should be strengthened. Thank you for your patience and understanding.

     

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