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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def first_phase(invec, outvec, N1, N2):
 """ This implements the first phase of the FFT decomposition, using the standard FFT many plans. Parameters invec : array The input array. outvec : array The output array. N1 : int Number of rows. N2 : int Number of columns. """

    global _theplan
    if _theplan is None:
        _theplan = plan_first_phase(N1, N2)
    fexecute(_theplan, invec.ptr, outvec.ptr)