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|    sci.math.symbolic    |    Symbolic algebra discussion    |    10,432 messages    |
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|    Message 8,556 of 10,432    |
|    clicliclic@freenet.de to clicliclic@freenet.de    |
|    Re: variable elimination from polynomial    |
|    07 Apr 14 19:41:37    |
      clicliclic@freenet.de schrieb:       >       > Waldek Hebisch schrieb:       > >       > > Using lexicographic order seem to take a lot of time and       > > memory. Using elimination order (homogeneous in blocks) in       > > FriCAS I get only one polynomial in elimination ideal:       > >       > > (x4^6+(25/16)*x4^4+(625/768)*x4^2+(15625/110592))*x3^9+(-4*x       ^7+(-245/48)*x4       > > ^5+(-2375/1152)*x4^3+(-3125/12288)*x4)*x3^8+((85/12)*x4^8+(5       7/72)*x4^6+(2309       > > 5/9216)*x4^4+(31625/73728)*x4^2+(3125/55296))*x3^7+((-787/10       )*x4^9+(-439/72)       > > *x4^7+(-19543/9216)*x4^5+(-63125/110592)*x4^3+(-625/8192)*x4       *x3^6+((691/144)       > > *x4^10+(119/36)*x4^8+(77375/55296)*x4^6+(28571/65536)*x4^4+(       075/73728)*x4^2+       > > (625/110592))*x3^5+((-151/72)*x4^11+(-179/144)*x4^9+(-6241/9       16)*x4^7+(-11683       > > 3/589824)*x4^5+(-32335/884736)*x4^3+(-125/24576)*x4)*x3^4+((       051/1728)*x4^12+       > > (773/2304)*x4^10+(15941/73728)*x4^8+(3059/49152)*x4^6+(5011/       94912)*x4^4+(235       > > /147456)*x4^2+(125/884736))*x3^3+((-65/576)*x4^13+(-37/576)*       4^11+(-9085/2211       > > 84)*x4^9+(-2309/147456)*x4^7+(-123/32768)*x4^5+(-187/442368)       x4^3+(-25/294912       > > )*x4)*x3^2+((7/576)*x4^14+(97/12288)*x4^12+(49/12288)*x4^10+       139/49152)*x4^8+       > > (91/442368)*x4^6+(79/589824)*x4^4+(1/98304)*x4^2)*x3+((-1/17       8)*x4^15+(-17/36       > > 864)*x4^13+(-5/36864)*x4^11+(-35/147456)*x4^9+(1/49152)*x4^7       (-1/65536)*x4^5)       > >       >       > Thanks for the private message. Meanwhile I have sped matters up by       > teaching Derive how to do resultants:       >       > resultant(f, g, x, n, m, a, h) := PROG(       > n := POLY_DEGREE(f, x),       > m := POLY_DEGREE(g, x),       > IF(n > m,       > RETURN (-1)^(n*m)*resultant(g, f, x),       > PROG(       > a := POLY_COEFF(f, x, n),       > IF(n = 0,       > RETURN a^m,       > PROG(       > h := REMAINDER(g, f, x),       > IF(IDENTICAL?(h, 0),       > RETURN 0,       > RETURN a^(m - POLY_DEGREE(h, x))*resultant(f, h, x)))))))       >       > Running resultant(resultant(lhs1, lhs2, x1), lhs3, x2) gives a result       > quite similar to yours, albeit squared:       >       > 4194304*(16*x3^9*(110592*x4^6 + 172800*x4^4 + 90000*x4^2 + 15625)       > - 48*x3^8*x4*(147456*x4^6 + 188160*x4^4 + 76000*x4^2 + 9375)       > + 8*x3^7*(1566720*x4^8 + 1618944*x4^6 + 554280*x4^4 + 94875*x4^2       > + 12500) - 8*x3^6*x4*(1611776*x4^8 + 1348608*x4^6 + 469032*x4^4       > + 126250*x4^2 + 16875) + x3^5*(8491008*x4^10 + 5849088*x4^8       > + 2476000*x4^6 + 771417*x4^4 + 97800*x4^2 + 10000)       > - x3^4*x4*(3710976*x4^10 + 2199552*x4^8 + 1198272*x4^6 + 350499*x4^4       > + 64670*x4^2 + 9000) + 2*x3^3*(538112*x4^12 + 296832*x4^10       > + 191292*x4^8 + 55062*x4^6 + 15033*x4^4 + 1410*x4^2 + 125)       > - 2*x3^2*x4*(99840*x4^12 + 56832*x4^10 + 36340*x4^8 + 13854*x4^6       > + 3321*x4^4 + 374*x4^2 + 75) + x3*x4^2*(21504*x4^12 + 13968*x4^10       > + 7056*x4^8 + 5004*x4^6 + 364*x4^4 + 237*x4^2 + 18)       > - x4^5*(1024*x4^10 + 816*x4^8 + 240*x4^6 + 420*x4^4 - 36*x4^2       > + 27))^2       >       > The squaring doesn't worry me, but that the factors are not fully       > proportional does very much. Could there be a bug somewhere?       >              Actually, when I copied the Groebner-basis result into Derive, some of       the coefficients were modified because spaces in numbers are interpreted       as products by Derive. In fact, the results do agree, normalization       apart! Good for Derive and for FriCAS.              Martin.              --- SoupGate-Win32 v1.05        * Origin: you cannot sedate... all the things you hate (1:229/2)    |
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