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calcorfft2.py

import numpy as np
from scipy.fftpack import fft,ifft
def CalCorFFT(sitesize,elecsize,basisseq,basissize,gsvec):
    numupseq=(np.tile(np.identity(basissize),(sitesize,1))*basisseq.reshape(basissize,2*sitesize)[:,:sitesize].T.reshape(sitesize*basissize,1)).reshape(sitesize,basissize,basissize)
    numdownseq=(np.tile(np.identity(basissize),(sitesize,1))*basisseq.reshape(basissize,2*sitesize)[:,sitesize:].T.reshape(sitesize*basissize,1)).reshape(sitesize,basissize,basissize)
    sumspin=numupseq+numdownseq
    densitycor=sumspin-(elecsize/sitesize)*np.tile(np.identity(basissize),(sitesize,1,1))
    spincor=(numupseq-numdownseq)/2
    nmq=fft(densitycor@gsvec,sitesize,axis=0)
    smq=fft(spincor@gsvec,sitesize,axis=0)
    nq=ifft(densitycor@gsvec,sitesize,axis=0)
    sq=ifft( spincor@gsvec,sitesize,axis=0)
    ftd=np.sum(nmq*nq,axis=1)
    fts=np.sum(smq*sq,axis=1)
    return ftd,fts