On Nov 22, 2011, at 3:40 PM, Monica Pisica wrote:
(edited out excessive white space)
I am trying to get a point of intersection between a
polyline and a straight line ….. and get the x and y coordinates of
this point.
For exemplification consider this:
set.seed(123)
k1 <-rnorm(100, mean=1.77, sd=3.33)
k1 <- sort(k1)
q1 <- rnorm(100, mean=2.37, sd=0.74)
q1 <- sort(q1, decreasing = TRUE)
plot(k1, q1, xlim <- c((min(k1)-5), (max(k1)+5)),
type="l")
ya <- 2
xa = -5
yb=4
xb=12
lines(c(xa, xb), c(ya, yb), col = 2)
# I want to get the x and y coordinates of the
# intersection of the 2 lines ….
m <- (ya-yb)/(xa-xb)
b <- ya-m*xa
ln <- loess(q1~k1)
lines(ln)
You should look at:
str(ln)
# then plot
lines(ln$x, ln$fitted, col="blue")
plot(approxfun(c(xa, xb), c(ya, yb)), add=TRUE, col="green")
plot(approxfun(ln$x, ln$fitted), col="orange", add=TRUE)
And think about minimizing the difference in distances between two
functions.
It is clear that the x, y will satisfy both linear
equations, y = m*x + b and the ln polyline ….. but while I can
visualize the
equation of the straight line – I have problems with the polyline. I
will appreciate
any ideas to solve this problem. I thought it a trivial solution but
it seems I
cannot see it.
Thanks,
Monica
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David Winsemius, MD
West Hartford, CT
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
