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Creating a Solar Model - Excel Help

  1. Mar 15, 2013 #1
    1. The problem statement, all variables and given/known data

    The problem given is...Calculate mI+1 and lI+1 at point xI+1 using equation (5), the values of the slopes at points xI+1 and xI from equation (4), and the values of mI and lI from the previous step.

    Here is a screenshot of my solar model

    solarmodel_zps169d03c0.png




    2. Relevant equations

    solarmodel2_zps8032b590.png


    3. The attempt at a solution

    I need help with columns I and J.

    For column I, I have the equation entered as =SUMPRODUCT(I2+1/2*(G3+G2)*B3-B2)

    For J I have =SUMPRODUCT(J2+1/2*(H3+H2)*B3-B2)

    and for some reason I'm getting negative values when as it goes down it should be getting closer to 1

    Thanks in advance!
     
  2. jcsd
  3. Mar 15, 2013 #2

    haruspex

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    You need parentheses around B3-B2.
    (Why do you need to use sumproduct? You're not using entire arrays of numbers to calculatd a single cell, are you?)
     
  4. Mar 15, 2013 #3
    Thank you so much! I knew it was something obvious that would make me look stupid ;)

    To your question...I'm not really sure. I'm excel illiterate and our professor expects us to use it without ever showing us anything.
     
  5. Mar 15, 2013 #4

    haruspex

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    Try removing the SUMPRODUCT() wrapper. I don't think it's doing anything.
     
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