Dear R users -- I have a simple question that I cannot find the answers in the archive email: how to plot a multivariate function if I know the coefficients already? For instance, if I like to plot a 3D fig of Pi against X and Y with the function Pi = a0 + a1X + a2Y, where a0, a1 & a2 are known. Can "curve" do this? So far, I have only seen univariate case. Thank you. Yihsu Chen
plot multivariate function with known coefficient.
2 messages · YIHSU CHEN, Gavin Simpson
On Tue, 2008-12-09 at 16:07 -0800, YIHSU CHEN wrote:
Dear R users -- I have a simple question that I cannot find the answers in the archive email: how to plot a multivariate function if I know the coefficients already? For instance, if I like to plot a 3D fig of Pi against X and Y with the function Pi = a0 + a1X + a2Y, where a0, a1 & a2 are known. Can "curve" do this? So far, I have only seen univariate case.
Not sure about a "curve3D()" but you can do this yourself using expand.grid (to give combinations of X and Y you wish to evaluate Pi at) and then use the vectorised nature of R to compute Pi for the combinations given known coefficients. E.g.: X <- seq(1, 100, by = 5) Y <- seq(1, 100, by = 5) XY <- expand.grid(X = X, Y = Y) a0 <- 2 a1 <- 0.5 a2 <- -0.3 Pi <- with(XY, a0 + (a1 * X) + (a2 * Y)) Pi <- matrix(Pi, ncol = length(X), byrow = TRUE) persp(X, Y, Pi) HTH G
Thank you. Yihsu Chen
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