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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 fit(self,Params0=None,grad_threshold=1e-2):
 """ fit a variance component model with the predefined design and the initialization and returns all the results """


        # GPVD initialization
        lik = limix.CLikNormalNULL()
        # Initial Params
        if Params0==None:
            n_params = self.C1.getNumberParams()
            n_params+= self.C2.getNumberParams()
            Params0 = SP.rand(n_params)
        # MultiGP Framework
        covar = []
        gp    = []
        mean  = []
        for i in range(self.N):
            covar.append(limix.CLinCombCF())
            covar[i].addCovariance(self.C1)
            covar[i].addCovariance(self.C2)
            coeff = SP.array([self.eigen[i],1])
            covar[i].setCoeff(coeff)
            mean.append(limix.CLinearMean(self.Yt[:,i],SP.eye(self.P)))
        gpVD = limix.CGPvarDecomp(covar[0],lik,mean[0],SP.ones(self.N),self.P,self.Yt,Params0)
        for i in range(self.N):
            gp.append(limix.CGPbase(covar[i],lik,mean[i]))
            gp[i].setY(self.Yt[:,i])
            gpVD.addGP(gp[i])
                
        # Optimization
        gpVD.initGPs()
        gpopt = limix.CGPopt(gpVD)
        LML0=-1.0*gpVD.LML()
        start_time = time.time()
        conv = gpopt.opt()
        time_train = time.time() - start_time
        LML=-1.0*gpVD.LML()
        LMLgrad = SP.linalg.norm(gpVD.LMLgrad()['covar'])
        Params = gpVD.getParams()['covar']
    
        # Check whether limix::CVarianceDecomposition.train() has converged
        if conv!=True or LMLgrad>grad_threshold or Params.max()>10:
            print('limix::CVarianceDecomposition::train has not converged')
            res=None
        else:
            res = {
                'Params0':          Params0,
                'Params':           Params,
                'LML':              SP.array([LML]),
                'LML0':             SP.array([LML0]),
                'LMLgrad':          SP.array([LMLgrad]),
                'time_train':       SP.array([time_train]),
                }
        return res
        pass