Failed to load resource: the server responded with a status of 502 (Bad Gateway) code example

Example: failed to load resource: the server responded with a status of 502 (bad gateway)

for j in x:
    if j == 1:
        index_for_multi_array = 0
    else:
        index_for_multi_array = 1

    q = con[j-1] # index 0 and 7 
    q = q * 1e-6
    m = mass[j-1]
    for i in range(1,int(bands[j-1])+1):
        #read parameters
        vc         = float(_1_wnum[index_for_multi_array][i-1])
        S0         = float(_1_int[index_for_multi_array][i-1] )
        gamma_air  = float(_1_abroad[index_for_multi_array][i-1])
        gamma_self = float(_1_sbroad[index_for_multi_array][i-1])
        n          = float(_1_abcoef[index_for_multi_array][i-1] )
        #resonance shape
        alpha_1  = float( (1.0- q) * gamma_air  + q * gamma_self ) * (P/P0) * ((T/T0) ** n)
        fv       = (alpha_1 / math.pi) * np.power((np.true_divide(v,vc)),2) * np.add((np.true_divide(1, np.power(v-vc,2) + alpha_1**2)) , np.true_divide(1,np.power((v+vc),2)+alpha_1**2))
        gv       = np.true_divide(v,vc) * pre_calculation / np.tanh(h*c*vc / (2*k*T)) * fv  
        S        = S0  #line intensity
        sigmav   = gv * S0
        qq       = q * P/R/T*NA
        kv       = P/P0*T0/T*qq*sigmav
        kvt[index_for_multi_array,:] = kvt[index_for_multi_array,:] + kv