add a basic Lotka-Volterra model to the model library

[papsti]

equations here

using the new model spec on the refactorcpp branch

[davidearn]

I like the idea of having L-V in the model library, but I have a few suggestions:

• include both L-V predator-prey and L-V competition models
• include the option for a carrying capacity in prey growth (so logistic rather than exponential growth of prey)
• include options for all three standard (Holling) functional responses

Making these options available as part of the model library would not take much extra effort and would potentially draw in a much larger ecological audience.

[stevencarlislewalker]

I agree completely @davidearn . Thank you for these suggestions.

Similarly, listening to Jane's talk last week made me want to include within-host immune response models.

[papsti]

i drafted a model definition for the basic lotka-voltera, but i'm running into errors. i'll push a branch off of refactorcpp with it so that we can troubleshoot.

[stevencarlislewalker]

@jfree-man has completed this task with 8a5d7c10be46208e635aa8abb75be0596f11f84f

[stevencarlislewalker]

Reopening, assigning to @jfree-man, and expanding scope as suggested by @davidearn.

I like the idea of having L-V in the model library, but I have a few suggestions:

* include both L-V predator-prey and L-V competition models

* include the option for a carrying capacity in prey growth (so logistic rather than exponential growth of prey)

* include options for all three standard (Holling) functional responses

Making these options available as part of the model library would not take much extra effort and would potentially draw in a much larger ecological audience.