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Question: polynomialinterpolation giving different results simply by changing variable?

Question:polynomialinterpolation giving different results simply by changing variable?

jccorreu 24 Maple
June 30 2006
0
intf12 := CurveFitting[PolynomialInterpolation](testfile[1..-1,1..2],z): eval(intf12, z=1); 54 0.1211007603 10 intf12 := CurveFitting[PolynomialInterpolation](testfile[1..-1,1..2],x): eval(intf12, x=1); 53 0.8 10 The only thing I changed was the variable from 'z' to 'x' I tried other names and they also gave me different answers once I evaluated. Is this a bug, known or unknown? Why would simply changing the variable name change the resulting equation? The answers are many orders of magnitude different than what I expect, which leads me to think that I am doing something incorrect. In the following data it can be seen that for a value of x=1, the resulting is y=-71.971859 Why is there no LinearInterpolation option? thanks all, James Following is a printlevel := 10 output for the 'x' version of the curvefit funtion: {--> enter CurveFitting:-PolynomialInterpolation, args = [[.9000, -69.887979], [.9200, -67.243299], [.9400, -64.809936], [.9500, -79.974336], [.9600, -62.579711], [.9800, -60.387775], [1.0000, -71.971859], [1.1000, -58.765899], [1.2000, -48.809024], [1.3000, -41.305696], [1.4000, -35.375931], [1.5000, -30.228975], [1.6000, -25.887651], [1.7000, -22.445696], [1.8000, -19.694000], [1.9000, -17.202900], [2.0000, -15.037239], [2.1000, -13.380959], [2.2000, -11.888100], [2.3000, -10.545859], [2.4000, -9.408000], [2.5000, -8.277500], [2.6000, -7.380976], [2.7000, -6.532864], [2.8000, -5.735351], [2.9000, -5.082000], [3.0000, -4.422171], [3.1000, -3.772571], [3.2000, -3.239236], [3.3000, -2.748900], [3.4000, -2.557504], [3.5000, -2.029919], [3.6000, -1.480956], [3.6500, -1.187319], [3.7000, -.885760], [3.7300, -.710563], [3.7500, -.523328], [3.8000, -.162893], [3.8300, .8575e-2], [3.8500, .182039], [3.8800, .387549], [3.9000, .614608], [3.9300, .825740], [3.9500, 1.028601], [3.9800, 1.209120], [4.0000, 1.331720], [4.0500, 1.463868], [4.1000, 1.460092], [4.1500, 1.332420], [4.2000, 1.140961], [4.3000, .839904], [4.4000, .590976], [4.5000, .360381], [4.6000, .202316], [4.7000, .59884e-1], [4.8000, -.18851e-1], [4.9000, -.80100e-1], [5.0000, -.137696], [5.2000, -.168675], [5.4000, -.183456], [5.6000, -.230736], [5.8000, -.288171], [6.0000, -.347275], [6.1000, -.381996], [6.2000, -.388416], [6.3000, -.365796], [6.4000, -.335616], [6.6000, -.286875], [6.8000, -.205939], [7.0000, -.111891], [7.2000, -.17037e-1], [7.4000, .80432e-1], [7.6000, .182001], [7.8000, .290700], [8.0000, .427008]], x {--> enter GetXYData, args = [[.9000, -69.887979], [.9200, -67.243299], [.9400, -64.809936], [.9500, -79.974336], [.9600, -62.579711], [.9800, -60.387775], [1.0000, -71.971859], [1.1000, -58.765899], [1.2000, -48.809024], [1.3000, -41.305696], [1.4000, -35.375931], [1.5000, -30.228975], [1.6000, -25.887651], [1.7000, -22.445696], [1.8000, -19.694000], [1.9000, -17.202900], [2.0000, -15.037239], [2.1000, -13.380959], [2.2000, -11.888100], [2.3000, -10.545859], [2.4000, -9.408000], [2.5000, -8.277500], [2.6000, -7.380976], [2.7000, -6.532864], [2.8000, -5.735351], [2.9000, -5.082000], [3.0000, -4.422171], [3.1000, -3.772571], [3.2000, -3.239236], [3.3000, -2.748900], [3.4000, -2.557504], [3.5000, -2.029919], [3.6000, -1.480956], [3.6500, -1.187319], [3.7000, -.885760], [3.7300, -.710563], [3.7500, -.523328], [3.8000, -.162893], [3.8300, .8575e-2], [3.8500, .182039], [3.8800, .387549], [3.9000, .614608], [3.9300, .825740], [3.9500, 1.028601], [3.9800, 1.209120], [4.0000, 1.331720], [4.0500, 1.463868], [4.1000, 1.460092], [4.1500, 1.332420], [4.2000, 1.140961], [4.3000, .839904], [4.4000, .590976], [4.5000, .360381], [4.6000, .202316], [4.7000, .59884e-1], [4.8000, -.18851e-1], [4.9000, -.80100e-1], [5.0000, -.137696], [5.2000, -.168675], [5.4000, -.183456], [5.6000, -.230736], [5.8000, -.288171], [6.0000, -.347275], [6.1000, -.381996], [6.2000, -.388416], [6.3000, -.365796], [6.4000, -.335616], [6.6000, -.286875], [6.8000, -.205939], [7.0000, -.111891], [7.2000, -.17037e-1], [7.4000, .80432e-1], [7.6000, .182001], [7.8000, .290700], [8.0000, .427008]], x
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