Re: BSpline function

*To*: mathgroup at smc.vnet.net*Subject*: [mg112824] Re: BSpline function*From*: "David Park" <djmpark at comcast.net>*Date*: Sat, 2 Oct 2010 05:44:17 -0400 (EDT)

It's a simple root finding problem but unfortunately neither FindRoot or Ted Ersek's RootSearch routine works well with BSplineFunction if we have to take the First or Last parts. But there is a simple solution: generate an InterpolatingFunction for the Last part and then do the root finding. pts = {{0.3, 0.74152}, {0.4, 0.650256}, {0.5, 0.588225}, {0.6, 0.541167}, {0.8, 0.473432}, {1., 0.425661}, {1.022, 0.42067}, {1.25, 0.380029}, {1.5, 0.346518}, {2., 0.300173}, {2.044, 0.297321}}; f = BSplineFunction[pts, SplineDegree -> 5]; g = FunctionInterpolation[Last[f[s]], {s, 0, 1}] Needs["Ersek`RootSearch`"] RootSearch[g[s] == s, {s, 0, 1}] {{s -> 0.446681}} Or FindRoot also works well here: sroot = FindRoot[g[s] == s, {s, 0.5}] {s -> 0.446681} Last[f[sroot]] == sroot True If I understand the question correctly. David Park djmpark at comcast.net http://home.comcast.net/~djmpark/ From: eric g [mailto:eric.phys at gmail.com] hello Group, I want to find the parameter of the spline function @ x=.9 in order to find the appropriate value of y? I can eye ball it using Table [{t,f[t]},{t,0,1,.01}] but I would like to get it straihgt... Also I would like to know what is the appropriate Spline-degree I should use? thnks in advance, Eric pts={{0.3, 0.74152}, {0.4, 0.650256}, {0.5, 0.588225}, {0.6, 0.541167}, {0.8, 0.473432}, {1., 0.425661}, {1.022, 0.42067}, {1.25, 0.380029}, {1.5, 0.346518}, {2., 0.300173}, {2.044, 0.297321}}; f= BSplineFunction[pts,SplineDegree->5]; f[?]={0.9,?}