Interpolation and plot doing strange things with mathematica 6 tia

*To*: mathgroup at smc.vnet.net*Subject*: [mg88964] Interpolation and plot doing strange things with mathematica 6 tia*From*: ratullochjk2 at gmail.com*Date*: Thu, 22 May 2008 02:38:27 -0400 (EDT)

Greetings All I run these commands that I've had plenty of help getting to work...but the plot doesn't follow the points, as you can see in the plot. At the end it just goes crazy and when I test the points with input s[0] output is -3.73293 why are the numbers so out of sync... at s[0] it should be -2 not -3.73293 I try increasing the number in the line N[FourierTrigSeries[f[x], x, 25, FourierParameters -> {-1, 1/138}]] (I've changed the number 25 to over 100 and the problem seems to get worse) See code below: In[89]:= data3 = {{0, -2}, {7, 1}, {10, 6}, {12, -2}, {18, -6}, {27, 6}, {34, 4}, {42, -6}, {49, -5}, {56, 4}, {62, 3}, {67, -5}, {70, -3}, {79, 3}, {83, 7}, {88, -3}, {89, -8}, {96, 7}, {105, 9}, {113, -8}, {122, -9}, {131, 9}, {132, 1}, {134, -9}, {138, -2}}; f = Interpolation[data3, PeriodicInterpolation -> True]; << "FourierSeries`" s[x_] = N[ FourierTrigSeries[f[x], x, 25, FourierParameters -> {-1, 1/138}]] discr = Interpolation[data3 /. {x_, y_} -> {x, y}, InterpolationOrder -> 1]; g[x_] = Piecewise[{{discr[x], 0 < x < 138}, {0, True}}]; Show[Plot[s[x], {x, 0, 138}, PlotStyle -> Red, PlotRange -> {-15, 15}], Plot[g[x], {x, 0, 138}, Filling -> Axis], ListPlot[data3, Filling -> Axis, PlotRange -> {0, 138}]] tia sal2