LarsPath-class: Constructor of LarsPath class
In MPAlars: lars algorithm

This class stores the results of lars and fusion algorithms.

nbStep: Number of steps of the algorithm.
variable: List of vector of size "step+1". The i+1-th item contains the index of non-zero coefficients at the i-th step.
coefficient: List of vector of size "step+1". The i+1-th item contains the non-zero coefficients at the i-th step.
lambda: Vector of length "step+1", containing the L1-norm of the coefficients at each step.
dropIndex: Vector of length "step" containing the index of the dropped variable at the i-th step, 0 means no variable has been dropped at this step.
addIndex: Vector of length "step" containing the index of the added variable at the i-th step, 0 means no variable has been added at this step.
mu: Intercept.
ignored: A vector containing index of ignored variables during the algorithm.
p: Total number of covariates.
fusion: If TRUE, results from MPA.fusion function.