Php-ml: PHP Machine Learning library, behavior issues

I'm using this library to predict numbers the thing is that I don't understand or don't get the problem in this piece of code, it always returns the same

>>> $SVR = new SVR(Kernel::LINEAR);
=> Phpml\Regression\SVR {#4304}
>>> $SVR->train([[1], [2], [3], [4],[5]],[3,1,2,3,2])
=> null
>>> $SVR->predict([6])
=> "2.1"
>>> $SVR->predict([7])
=> "2.1"
>>> $SVR->predict([8])
=> "2.1"
>>> $SVR->predict([9])
=> "2.1"