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Functions

The procedures `TheFunction` and `IntervalFunction` should be
user written. They return the value
of the equations (either as a vector of `REAL`
or as a vector of `INTERVAL`, see 2.3.4.3) for given values
or intervals
for the unknowns.
They take one argument which is the vector of `REAL` which
describe the unknowns.
In the same way the procedures `Gradient` and `IntervalGradient` should be
user written. They return the Jacobian matrix of the system of equations
of the equations
(either as a matrix of `REAL`
or as a matrix of `INTERVAL`) for given
values of the unknowns.
The `Gradient` procedure
take one argument which is the vector of `REAL` which
describe the unknowns.
The `IntervalGradient` procedure has three arguments and is
described in section 2.4.2.2.

Jean-Pierre Merlet
2012-12-20