Confused by output from Polyval











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I have some data from which I have fitted a 2nd order polynomial using numpy.polynomial.polynomial.polyfit



data_fit = poly.polyfit(length_spline_a, temp_spline_b, 2)


I am examining changes in length, and have a list of 10% changes in length



len_steps = 0.0, -0.012573565669572757, -0.025147131339145513, -0.03772069700871827...

print (len(len_steps)

>>>>11


My assumption was that polyval would solve for y for each of the x values in the len_steps list



y_data = poly.polyval(data_fit, len_steps)


However this provides a list with only 3 data points rather than the 11 I expected. 



print(y_data)

>>>>[-5.34112443e+21 -2.50395581e+28 -6.75169134e+28]


Have I mis understood the purpose of polyval or have I done something wrong?






python python-3.x numpy polynomials







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    up vote
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    down vote

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    I have some data from which I have fitted a 2nd order polynomial using numpy.polynomial.polynomial.polyfit



    data_fit = poly.polyfit(length_spline_a, temp_spline_b, 2)


    I am examining changes in length, and have a list of 10% changes in length



    len_steps = 0.0, -0.012573565669572757, -0.025147131339145513, -0.03772069700871827...
    
print (len(len_steps)
    
>>>>11


    My assumption was that polyval would solve for y for each of the x values in the len_steps list



    y_data = poly.polyval(data_fit, len_steps)


    However this provides a list with only 3 data points rather than the 11 I expected. 



    print(y_data)
    
>>>>[-5.34112443e+21 -2.50395581e+28 -6.75169134e+28]


    Have I mis understood the purpose of polyval or have I done something wrong?






    python python-3.x numpy polynomials







    share|improve this question


























      up vote
      1
      down vote

      favorite









      up vote
      1
      down vote

      favorite











      I have some data from which I have fitted a 2nd order polynomial using numpy.polynomial.polynomial.polyfit



      data_fit = poly.polyfit(length_spline_a, temp_spline_b, 2)


      I am examining changes in length, and have a list of 10% changes in length



      len_steps = 0.0, -0.012573565669572757, -0.025147131339145513, -0.03772069700871827...
      
print (len(len_steps)
      
>>>>11


      My assumption was that polyval would solve for y for each of the x values in the len_steps list



      y_data = poly.polyval(data_fit, len_steps)


      However this provides a list with only 3 data points rather than the 11 I expected. 



      print(y_data)
      
>>>>[-5.34112443e+21 -2.50395581e+28 -6.75169134e+28]


      Have I mis understood the purpose of polyval or have I done something wrong?






      python python-3.x numpy polynomials







      share|improve this question















      I have some data from which I have fitted a 2nd order polynomial using numpy.polynomial.polynomial.polyfit



      data_fit = poly.polyfit(length_spline_a, temp_spline_b, 2)


      I am examining changes in length, and have a list of 10% changes in length



      len_steps = 0.0, -0.012573565669572757, -0.025147131339145513, -0.03772069700871827...
      
print (len(len_steps)
      
>>>>11


      My assumption was that polyval would solve for y for each of the x values in the len_steps list



      y_data = poly.polyval(data_fit, len_steps)


      However this provides a list with only 3 data points rather than the 11 I expected. 



      print(y_data)
      
>>>>[-5.34112443e+21 -2.50395581e+28 -6.75169134e+28]


      Have I mis understood the purpose of polyval or have I done something wrong?






      python python-3.x numpy polynomials




      python python-3.x numpy polynomials






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      edited Nov 8 at 11:16

























      asked Nov 8 at 10:46









      nick.sculthorpe

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          The output works if I reverse the list order to y_data = poly.polyval(len_steps, data_fit) which is actually clear now I re-read the documents. I think I was using the np.polyval syntax which expects the coefs first.






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            The output works if I reverse the list order to y_data = poly.polyval(len_steps, data_fit) which is actually clear now I re-read the documents. I think I was using the np.polyval syntax which expects the coefs first.






            share|improve this answer

























              up vote
              0
              down vote













              The output works if I reverse the list order to y_data = poly.polyval(len_steps, data_fit) which is actually clear now I re-read the documents. I think I was using the np.polyval syntax which expects the coefs first.






              share|improve this answer























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                up vote
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                down vote









                The output works if I reverse the list order to y_data = poly.polyval(len_steps, data_fit) which is actually clear now I re-read the documents. I think I was using the np.polyval syntax which expects the coefs first.






                share|improve this answer












                The output works if I reverse the list order to y_data = poly.polyval(len_steps, data_fit) which is actually clear now I re-read the documents. I think I was using the np.polyval syntax which expects the coefs first.







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                answered Nov 8 at 11:26









                nick.sculthorpe

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