3rd order equations



*Dear Richard Fateman,

Thank you very much for your answer which helped a lot.

Best regards,

Esben Byskov
*

Esben Byskov, Ph.D., Dr.Techn.
Professor Emeritus of Structural Analysis
Department of Civil Engineering
Aalborg University
Sohngaardsholmsvej 57
DK-9000 Aalborg
Denmark

Phone:   +45 3963 7328
          +45 2178 8365
e-mail:  eb at civil.aau.dk
          esben at annegrete.dk



On 08/16/2013 06:27 PM, Richard Fateman wrote:
> On 8/16/2013 5:56 AM, Esben Byskov wrote:
>> *Maybe somebody can help.
>>
>> I have tried to solve the following rather simple equation using maxima:
>>
>> (%i1) Eq: -2*q^3+3*q-1.357008100494576;
>> (%o1)                  - 2 q  + 3 q - 1.357008100494576
>>
>> (%i2) solve(Eq,q);*
> *first mistake.  Solve finds exact solutions. It is unlikely that 
> 1.35....576 is known exactly, but solve
> assumes it is precisely a certain rational number, and goes from there.
>
> try
>
> allroots(Eq);
>
> or
>
> realroots(Eq);    --- for rational approximations of guaranteed error 
> bounds.
>
>
> *