Can Excel describe a function in two variables: y = f(x,z)

[Guest]

I have two independent variables (inputs: x, z) and one output: y. I have
the data for all three variables in columns in an Excel 2000 worksheet. Can
Excel graph and fit an equation to this data? I want an equation of the form
y = f(x,z). Thanks!

 

[Bernard Liengme]

Not unless you have a starting function. For example if y=ax^2 - bz^3 we
could use Solver to find the best fit values for a and b
Tell us more
best wishes

 

[Guest]

No, I have no function yet, just data... I have over 100 ordered triples
(x,y,z) and would like to fit an equation to this data. Suggestions?
Thanks,
Cece

 

[Guest]

Hi Cece,

Perhaps there is an approximate workaround (although a formal solver would
be preferable imho).
The y series can be plotted against x as a (xy) scattergraph. A trendline
(Type polynomial perhaps) can be added and under the Options tab its equation
can be displayed on the chart (accuracy depending on the type of the trend,
and e.g. the order of the polynomial). The equation font size usually needs
increasing from something like 8.
The same can be done for the y series against the z series.
I think that from the resulting equations y = f(x) and y = f(z) it would be
possible to construct y = f(x,z), e.g. add f(x) and f(z) and divide them by
2, or take the sqrt of f(x)*f(z) (?)

I don't think standard Excel can plot y = f(x,z) (perhaps Excel 2007 or an
add-in ? or, if not, other graph plotting s/w). (If Excel 2007 can plot 3d
then perhaps it can also add a trend and display its equation).

HTH
Anthony