Direct Plotting of equations on charts and Pivot Charts
It would be useful to be able to plot an equation on a Pivot Chart (or regular chart) without generating the data that drives it.
The usecase that makes me think of this is as follows:
 I have some data representing measurements.
 There is an expected or theoretical curve shape that the measurements should roughly follow.
 I want to plot the data (scatter points) and the theoretical curve (or curves).
What I do:
 This works reasonably well if I have lots of data points as for each x I can calculate the theoretical y and then that becomes part of the TheoreticalCurve series, which will be plotted as a smooth line.
 However it doesn't work well if the measurement data is more sparse. Then I need to generate a separate set of x values (say a series of values a fixed interval apart within the bounds of ) so that I can draw the smooth line. This latter approach is not very scalable and could better be automated within the chart.
I'm especially interested in seeing this if nonaggregate Pivot Scatter plots become available (http://excel.uservoice.com/forums/304921excelforwindowsdesktopapplication/suggestions/9946839scatterchartswithgroupbyfromthirddataserie). Because what's the next thing you want to do after plotting some data on a scatter chart? Very often the answer is 'draw some lines with certain equations over it'.
Thanks for posting this. We’ll definitely consider it in the planning for our next round of features. Please continue voting on this feature request which will increase its likelihood of getting in the product.
Thanks,
Scott [MSFT]
1 comment

Kenneth Barber commented
I'd love to have equationbased graphs in Excel. Especially 3D surfaces.