class Packer:
    """A compression object used to speed up model calculations.

    Often used in conjunction with crossvalidation and perturbations
    analysis. 
    """
    def __init__(self,array):
        self._shape = array.shape
        self._array = array
        self._packed_data = None
        
    def expand(self,a):
        if self._inflater!=None:
            return dot(self._inflater,a)
        
    def collapse(self,axis=None,mode='svd'):
        if not axis:
            axis = argmin(self._array.shape) # default is the smallest dim

        if axis == 1:
            self._array = self._array.T
        u, s, vt = svd(self._array,full_matrices=0)
        self._inflater = vt.T
        self._packed_data = u*s
        return self._packed_data

    def get_packed_data(self):
        return self._packed_data