Automatic set-up for size selex 6 and age selex 17 and others

[k-doering-NOAA]

Imported from redmine, Issue #17504 Opened by teresa.amar on 2016-04-05 Status when imported: New

Add automatic set-up for size selex 6 (non-parametric) and age selex 17 (random walk)

Pattern 6 (non-parametric size selectivity) number of parameters: 2 + special value This pattern uses a set of linear segments. The first waypoint is at Length = p1 and the last waypoint is at Length=p2. The total number of waypoints is specified by the value of the Special factor in the selectivity set-up, so the N intervals is one less than the number of waypoints. Intermediate waypoints are located at equidistant intervals between p1 and p2. Parameters 3 to N are the selectivity values at the waypoints, entered as logistic, e.g. 1/(1+exp(-x)). Ramps from –10 to p3 if L<p1. Constant at pN if L>p2.

Pattern 17 (age selectivity) number of parameters: Nages + 1 This selectivity pattern provides for a random walk in ln(selectivity). In typical usage:

• First parameter (for age 0) could have a value of -1000 so that the age 0 fish would get a selectivity of 0.0;
• Second parameter (for age 1) could have a value of 0.0 and not be estimated, so age 1 is the reference age against which subsequent changes occur;
• Next parameters get estimated values. To assure that selectivity increases for the younger ages, the parameter min for these parameters could be set to 0.0 or a slightly negative value.
• If dome-shaped selectivity is expected, then the parameters for older ages could have a range with the max set to 0.0 so they cannot increase further.
• To keep selectivity at a particular age the same as selectivity at the next younger age, set its parameter value to 0.0 and not estimated. This allows for all older ages to have the same selectivity.
• To keep a constant rate of change in selectivity across a range of ages, use the - 999 flag to keep the same rate of change in ln(selectivity) as for the previous age.