# Exponential or not?

1. Sep 22, 2014

### nordmoon

I have a curve I obtained in COMSOL representing a electric field for m structure. I have to figure how to determine when the curve starts to become exponential decaying at certain regions.

Any idea how to determine when the curve starts becoming exponential decaying from a plot?

2. Sep 22, 2014

### mathman

Plot the curve on semi-log paper. A straight line there will be equivalent to exponential on a linear plot.

3. Sep 29, 2014

### nordmoon

How do I see when the plot is no longer linear? I am estimating the curves R2-values (coefficient of determination).

I get values like,

1.0
0.9998
0.9953
0.9915
0.95

etc

I just don't know how to determine when it stops being linear. Do you have any suggestions?

4. Sep 29, 2014

### mathman

I don't understand your concern. When you plot it and it starts to curve then it is no longer linear.

5. Sep 29, 2014

### WWGD

Low values of R^2 go together with a low (linear) goodness-of-fit .