[R] plotting a bivariate quadratic curve
Hi, I would like to plot a x,y curve described by the equation : Ax^2 + Bx + Cy^2 + Dy + E == 0 (A,B,C,D,E are constants) This sounds like quite the common task but haven't been able to figure out how to do this. Could you please help ? I am new to R so probably missing something basic. Thanks __ 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.
Re: [R] plotting a bivariate quadratic curve
On 11-11-12 5:50 AM, Yackov Lubarsky wrote: Hi, I would like to plot a x,y curve described by the equation : Ax^2 + Bx + Cy^2 + Dy + E == 0 (A,B,C,D,E are constants) This sounds like quite the common task but haven't been able to figure out how to do this. Could you please help ? I am new to R so probably missing something basic. R is not very good at that, but one way to do it is to draw a contour plot of the bivariate function, with a single contour at level 0. For example, A - B - C - D - 1 E - -1 x - y - seq(-3, 3, len=100) z - outer(x, y, function(x, y) A*x^2 + B*x + C*y^2 + D*y + E) contour(x, y, z, levels=0, drawLabels=FALSE) Another would be to solve for y as a function of x, and draw both branches. Duncan Murdoch __ 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.
Re: [R] plotting a bivariate quadratic curve
On Sat, Nov 12, 2011 at 10:50 AM, Yackov Lubarsky yluba...@gmail.com wrote: Hi, I would like to plot a x,y curve described by the equation : Ax^2 + Bx + Cy^2 + Dy + E == 0 (A,B,C,D,E are constants) This sounds like quite the common task but haven't been able to figure out how to do this. Could you please help ? I am new to R so probably missing something basic. What you may be missing was all figured out by the ancient Greeks and they didnt even have R in their alphabet! You've got this: http://mathworld.wolfram.com/QuadraticCurve.html but with b=0. I'm not sure how many of the awkward cases (line pairs, imaginary everything) disappear with b=0, but you can compute the Delta, I, J, and K determinants to figure it out. Then set theta to seq(0,2*pi,len=100) and compute r from the polar equation form. Plot r*cos(theta), r*sin(theta)... Confession: its been a long time since I did maths like this (forgive me father, for I have not sin'd). Barry __ 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.
