Chapter 15 . Evolved Predictive Rules for Algal Dynamics
2
3
Ir PHOSPHATE 15 low
5 THEN CHL-A 15 high
Description
Value
Transparency is high
Transp > lIOcm
Nitrate is high
N03> 5771.Lg/l
Nitrate is low
N03 < 577~g/1
Phosphate is low
P04 < 34~g/1
Chlorophyll-a is low
Chl-a = 34mg/l
Chlorophyll-a is medium
Chl-a = 55mg/l
Chlorophyll-a is high
Chl-a = 67mg/l
Chlorophyll-a is very high
Chl-a = 97mg/l
Chlorophyll-a is extremely high Chl-a = 140mg/l
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Figure 15.4. A rule set for input set 2 discovered by the evolutionary algorithm.
Note: Chl-a measured in p.gll.
Input set 1 contains all of the available input parameters. The variance of the
RMSE for this data set is high, which is possibly due to the higher degree of
freedom available from the larger number of input parameters when producing
models with this dataset. A random rule set from input set 1 is shown in Figure
15.5.
The different model structures produced qualitatively different predictions. In
particular, the timing of high algal abundance was picked up by different model
structures differently. The model detailed in Figure 15.5 produced the prediction
on the unseen testing years of 1986 and 1993 shown in Figure 15.6 and 15.7. This
model had a very good RMSE = 35.76.