saving a variable column name in text via python

col = ['rss','intercept'] + ['coef_x_%d'%i for i in range(1,16)]
ind = ['model_pow_%d'%i for i in range(1,16)]
coef_matrix_simple = pd.DataFrame(index=ind, columns=col)

for i in range(1,16):
   coef_matrix_simple.iloc[i-1,0:i+2] = linear_regression(df, power=i, models_to_plot=models_to_plot)

pd.options.display.float_format = '{:,.2g}'.format
coef_matrix_simple

np.savetxt('output.csv', coef_matrix_simple,  delimiter =" ")

I want to save the coef_matrix_simple along with col values as column name and ind values in the csv file. saving the coef_matrix_simple gives only numbers without any column name.