Creating a Solar Model - Excel Help

1. Mar 15, 2013

PeteWheatstraw

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

2. Relevant equations

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

2. Mar 15, 2013

haruspex

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?)

3. Mar 15, 2013

PeteWheatstraw

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.

4. Mar 15, 2013

haruspex

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