One way is to use convolution (?convolve): If A(x) = a_p*x^p + ... + a_1*x + a_0 and B(x) = b_q*x^q + ... + b_1*x + b_0 and if C(x) = A(x)*B(x) = c_(p+q)*x^(p+q) + ... + c_0 then c = convolve(a,rev(b),type="open") where c is the vector (c_(p+q),...,c_0), a is (a_p,...,a_0) and b is (b_q,...,b_0). In your case:
> a <- c(1,-3) > b <- c(1,3) > c <- convolve(a,rev(b),type="open") > c [1] 1.00000e+00 -6.49654e-16 -9.00000e+00 Note that the coefficient of x is not exactly 0 due to the use of fft to compute convolutions. --- On Thu, 16/10/08, Erin Hodgess <[EMAIL PROTECTED]> wrote: > From: Erin Hodgess <[EMAIL PROTECTED]> > Subject: [R] a really simple question on polynomial multiplication > To: "R Help" <r-help@r-project.org> > Received: Thursday, 16 October, 2008, 8:44 AM > Dear R people: > > Is there a way to perform simple polynomial multiplication; > that is, > something like > (x - 3) * (x + 3) = x^2 - 9, please? > > I looked in poly and polyroot and expression. There used > to be a > package that had this, maybe? > > thanks, > Erin > > > -- > Erin Hodgess > Associate Professor > Department of Computer and Mathematical Sciences > University of Houston - Downtown > mailto: [EMAIL PROTECTED] > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, > reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
