Hi all, Thanks for the replies, but I realize I've done a bad job explaining my problem. To help, I've created some sample data to explain the problem.
df <- data.frame(x=c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12), y=c(109, 232, 363, 496, 625, 744, 847, 928, 981, 1000, 979, 912), s=c(109, 341, 704, 1200, 1825, 2569, 3416, 4344, 5325, 6325, 7304, 8216)) In this data frame, y results from y = x * b1 + x^2 * b2 + x^3 * b3 and s is sum of the current y and all previous y (s3 = y1 + y2 + y3). I know I can find b1, b2 and b3 using: lm(y ~ 0 + x + I(x^2) + I(x^3), data=df) yielding... Coefficients: x I(x^2) I(x^3) 100 10 -1 However, I need to find b1, b2 and b3 using the s column. The reason being, I don't actually know the values of y in the actual data set. And in the actual data, I only have a few of the values. Imagine this data is being used a reward schedule for like a loyalty points program. y represents the number of points needed for each level while s is the total number of points to reach that level. In the real problem, my data looks more like this: d <- data.frame(x=c(1, 4, 9, 12), s=c(109, 1200, 5325, 8216)) Where I need to use a few sample points to help define the parameters of the curve. thanks again and hopefully this makes the problem a bit clearer. robbie On Fri, May 18, 2012 at 7:40 PM, David Winsemius <dwinsem...@comcast.net>wrote: > > On May 18, 2012, at 1:44 PM, Robbie Edwards wrote: > > Hi all, >> >> I'm trying to model some data where the y is defined by >> >> y = summation[1 to 50] B1 * x + B2 * x^2 + B3 * x^3 >> >> Hopefully that reads clearly for email. >> >> > cumsum( rowSums( cbind(B1 * x, B2 * x^2, B3 * x^3))) > > > > Anyway, if it wasn't for the summation, I know I would do it like this >> >> lm(y ~ x + x2 + x3) >> >> Where x2 and x3 are x^2 and x^3. >> >> However, since each value of x is related to the previous values of x, I >> don't know how to do this. Any help is greatly appreciated. >> >> >> > > David Winsemius, MD > West Hartford, CT > > [[alternative HTML version deleted]] ______________________________________________ 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.