[R] determine length of bivariate polynomial

[Nicolas Schuck]

I was thinking of an analytical solution, but using diff() works great as well!

thanks for help,
nico 

On Nov 10, 2011, at 2:55 AM, R. Michael Weylandt wrote:

> I think this will do it:
> 
> sum(sqrt(diff(x.pred)^2 + diff(y.pred)^2))
> 
> Michael
> 
> On Tue, Nov 8, 2011 at 11:34 AM, Nicolas Schuck
> <nico.schuck at googlemail.com> wrote:
>> Dear R-community,
>> 
>> I have a fitted bivariate polynomial, i.e:
>> 
>> fit = lm(cbind(x, y)~poly(t, 15))
>> 
>> and I would like to determine the length of the line in the interval t =
>> [a, b]. Obviously, I could use predict and go through all the points, i.e.
>> 
>> for (t in a:(b-1)) {
>> length = length + sqrt((x.pred[t] - x.pred[t+1])^2 + (y.pred[t] -
>> y.pred[t+1])^2)
>> }
>> 
>> but that would take very long given the amount of data I have. Do you know
>> of any better solutions?
>> 
>> Many thanks!
>> Nicolas
>> 
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>> 
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