def __init__(self, filename, tst = False):
        self.vx, self.vy = read_kl(filename)
        self.f_interp = interp1d(self.vx, self.vy, kind = 'linear', bounds_error=False)
        # Test:
        if tst:
            x_dense = np.linspace(-1., 15., 200)
            y_dense = []
            for xx in x_dense:
                y_dense.append(self.f_interp(xx))            
            lines = plt.plot( x_dense, y_dense )
            plt.show()