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irreducibility test

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mmavrop
mmavrop el 14 de Mzo. de 2012
Editada: sqw el 20 de En. de 2014
Hi all,
I would like to ask you, about the function irreducible.. http://www.mathworks.com/help/toolbox/mupad/stdlib/irreducible.html
I want to check if a polynomial is irreducible, but I have problem on how to declare the polynomial..I tried the examples o the abov link but matlab returns " ??? Undefined function or variable 'x'."..

Respuesta aceptada

Walter Roberson
Walter Roberson el 14 de Mzo. de 2012
syms x
evalin(symengine, 'irreducible', x^2 - 2)

Más respuestas (3)

Stefan Wehmeier
Stefan Wehmeier el 26 de Mzo. de 2012
You have to declare it as a polynomial over GaloisField, e.g.
F = evalin(symengine, 'poly(x^2-2, Dom::GaloisField(5^7)))
feval(symengine, 'irreducible', F)
  2 comentarios
mmavrop
mmavrop el 26 de Mzo. de 2012
thanks a lot!
sqw
sqw el 20 de En. de 2014
Editada: sqw el 20 de En. de 2014
hi I want use this function for a loop of polynomial but I cant change the polynomial with symbolic variableas.
for example i want this: syms x z=x^a(n,1)+x^a(n,2)+1 for i=1 we have z=x^19+x^12+1 %%a is a vector and change base for i=1:n i want check the z polynomial is irreducible or not?
F = evalin(symengine, 'poly(z,Dom::GaloisField(2))') F =
poly(z, [z], Dom::GaloisField(2, 1, poly(X7, [X7], IntMod(2)))) feval(symengine, 'irreducible', F)
ans =
TRUE
but this polynomial in not irreducible
the mistake of this answer come from [z] instead of [x]!!!!
please help me to solve it

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mmavrop
mmavrop el 14 de Mzo. de 2012
thank you Walter! I tried your answer and matlab returned "`proc irreducible(p) ... end`" in both cases, (x^2 - 2) and (x^2 + 2).. What am I doing wrong? I am using matlab R2009b..
  2 comentarios
Walter Roberson
Walter Roberson el 14 de Mzo. de 2012
Hmmm.... Say, are you perhaps using the Maple symbolic engine? That was still possible in R2009b even though MuPAD was the default. Your ending of the procedure with "end" is a clue, in that MuPAD ends its procedures with "end_proc" but Maple ends with "end".
The internal Maple name for the procedure was irreduc so you could _try_
feval(symengine, 'irreduc', x^2 - 2)
If that doesn't work, go back to irreducible but with feval
Alexander
Alexander el 15 de Mzo. de 2012
feval did the trick for me:
>> syms x
>> feval(symengine, 'irreducible', x^2 + 2)
ans =
TRUE

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mmavrop
mmavrop el 24 de Mzo. de 2012
Thank you so much both! it works! May I ask an other question? Is there a way to find out if a polynomial over galois field is irreducible?

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