Add "linear_ode_generation"

A symbolic link to scripts of generating a linear ODE system.
Create "objective.R"

Define a function which takes eigen-values of coefficient matrix
as input,
and output the optimal residue.
Used as the objective function for algorithm seeking for optimal
eigen-values.

Argument "type" of value "post" is yet implemented.

Create "objective_test.R" as a testing script.