[R] finding the intersection of two vectors
David Winsemius
dwinsemius at comcast.net
Wed Jul 6 23:50:38 CEST 2011
On Jul 6, 2011, at 4:43 PM, Data Analytics Corp. wrote:
> Hi,
>
> Suppose I have two vectors, not necessarily the same length (in
> fact, they usually are different lengths): y.1 that has increasing
> values between 0 and 1; y.2 that has decreasing values between 1.0
> and 0. You can picture these as being supply (= y.1) and demand (=
> y.2) curves from economics. I typically plot these vectors on the
> same graph against a common x variable, which happens to be price
> for what I do. The price variable runs from, say, $0 to $25. When
> I plot y.1 and y.2, I've been eye-balling a vertical line at a price
> point where y.1 intersects y.2. I'm now tired of eye-balling a line
> through the intersection -- takes too much time to get it right or
> just close enough. I can't figure out how to find the price value
> at which the two curves intersect. Going back to the economics
> interpretation, I want the price where supply equals demand. Any
> suggestions as to how I can find that price point in R? Any
> functions that help?
?approxfun # or..
?splinefun # should allow you to make two functions and then solve
for the X taht minimizes the difference.
--
David Winsemius, MD
West Hartford, CT
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