def sum_emat(seq, emat):
    """
    Retrieve and sum the energy matrix values for a given sequence variant and matrix.
    
    Parameters
    ----------
    seq : string
    
    emat : pd.DataFrame with columns A T C G
    
    Returns
    ---------
    sum : float
    """
    
    mat_vals = []
    
    for ind,char in enumerate(seq, start = 0):
        #print(ind)
        #print(char)
        mat_vals.append(emat.iloc[ind][char])
        
    return(sum(mat_vals))