code: def interact_GxG(pheno,snps1,snps2=None,K=None,covs=None):
      
      if K is None:
          K=SP.eye(N)
      N=snps1.shape[0]
      if snps2 is None:
          snps2 = snps1
      return interact_GxE(snps=snps1,pheno=pheno,env=snps2,covs=covs,K=K)
docs: Epistasis test between two sets of SNPs
  
      Args:
          pheno:  [N x 1] SP.array of 1 phenotype for N individuals
          snps1:  [N x S1] SP.array of S1 SNPs for N individuals
          snps2:  [N x S2] SP.array of S2 SNPs for N individuals
          K:      [N x N] SP.array of LMM-covariance/kinship koefficients (optional)
                          If not provided, then linear regression analysis is performed
          covs:   [N x D] SP.array of D covariates for N individuals
  
      Returns:
          pv:     [S2 x S1] SP.array of P values for epistasis tests beten all SNPs in
                  snps1 and snps2