On Apr 28, 2010, at 6:04 AM, Yann wrote:

This at least documented:

sage: R.<x>=ZZ[]
sage: f = x^3+x+1
sage: f.mod?
...
      When little is implemented about a given ring, then mod may
return
      simply return f.  For example, reduction is not implemented for
      ZZ[x] yet. (TODO!)

         sage: R.<x> = PolynomialRing(ZZ)
sage: f = x^3 + x + 1 sage:
         f.mod(x + 1) x^3 + x + 1

Ouch. We should be at least trying f % q, or even f.quo_rem()[1], which is much better implemented across the board. (I didn't even know there was a mod method.)

- Robert



On Apr 28, 2:03 pm, Michael Rybalkin <[email protected]>
wrote:
I faced with a problem with polynomial mod

This is example from manual: mod?
sage: R.<x> = QQ['x'];
sage: f = x^3 + x + 1
sage: f.mod(x + 1)
Result is -1

But changing from field QQ to ring ZZ causes mod to do nothing:
sage: R.<x> = ZZ['x'];
sage: f = x^3 + x + 1
sage: f.mod(x + 1)
Result is x^3 + x + 1

Mod function doesn't do anything. And is doesn't work for polynomials
over IntegerModRing also and for symbolic polynomial ring.

sage: var('x')
sage: f = x^3 + x + 1
sage: f.mod(x + 1)
Result is x^3 + x + 1

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