'''MAIN PROGRAM'''
def y(params, x):
    y = np.empty(len(x))
    for i in range(len(x)):
        y[i] = params[0]*math.sin(x[i]) + params[1]*math.cos(x[i]) + \
                    params[2]*math.sin(2*x[i]) + params[3]*math.cos(2*x[i])
    return y

params_QR = lstsq_QR(A, y_values)
params_SVD = lstsq_SVD(A, y_values)

y_QR = y(params_QR, x_values)
y_SVD = y(params_SVD, x_values)

plt.plot(x_values, y_values, 'bs', \
         x_values, y_QR, 'r--', \
         x_values, y_SVD, 'g^')
#plt.close()


# min ||Ax - b||:
min_diff = sl.norm(y_values - y_QR, 2)
testt = sl.norm(y_QR - y_SVD, 2)