The first issue is that there are many possible representations for an Increasing metafeature. Most of them would have at least four parameters. For example one possible representation for an Increasing event would be: (start time, end time, start value, end value). However, another representation is possible using the following tuple: (midtime, duration, average value, gradient). Both of these representations give us information about the underlying features, and it is easy to convert from one to the other. Both of these representations are shown in Figure 4.7.
Furthermore, these are but two of a number of possibilities. Hybrids of the above exist, for example an increasing event could also be represented as: (start time, end time, gradient, average), or (middle time, duration, start value, end value). What then, is the appropriate representation? Common engineering practice would suggest that the basis for selecting a particular representation should at least include the following criteria:
