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Conference rusure::math

Title:Mathematics at DEC
Moderator:RUSURE::EDP
Created:Mon Feb 03 1986
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:2083
Total number of notes:14613

79.0. "Squaring makes smaller" by HARE::STAN () Mon Jun 11 1984 14:58

Is there a polynomial whose square has fewer terms?

Are there two polynomials with m and n terms, respectively,
whose product has fewer than min(m,n) terms?
T.RTitleUserPersonal
Name
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79.1AURORA::HALLYBMon Jun 11 1984 21:442
Presumably Stan is referring to polynomials over the reals.  An easy
counterexample (otherwise) would be 2x+y, over the integers modulo 4.
79.2HARE::STANTue Jun 12 1984 02:241
I intended that the coefficients be (non-zero) complex numbers.
79.3HARE::GILBERTTue Jun 12 1984 18:0010
Here are two polynomials with 4 terms each, and a product with 2 terms:

	     3     2       2    3            2         2
	p = x  - 2x y + 2xy  - y  = (x - y)(x  - xy + y )

	     3     2       2    3            2         2
	q = x  + 2x y + 2xy  + y  = (x + y)(x  + xy + y )

	     6    6
       pq = x  - y 
79.4ORPHAN::BRETTTue Jun 12 1984 19:504
Okay, now for only one variable....

/Bevin
79.5TURTLE::STANTue Jun 12 1984 22:371
Let y=1.