Square-law based RBF kernel What is the Square-law based RBF kernel (SQ-RBF)? The definition in the table at the Wikipedia article Activation Function looks wrong, since it says

y = 
     1 - x^2/2     for |x| &lt;= 1
     2 - (2-x^2)/2 for 1 &lt; |x| &lt;= 2
     0             for |x| &gt; 2


but this makes it discontinuous at x = 1
That is indeed quite odd. I can't really find many other sources on SQ-RBF, except here, where the definition differs from wikipedia, but when I plot this, it does not recover the image they show. However, if you define

y =
    1 - x^2/2        for |x| &lt;= 1
    0.5*(|x|-2)^2    for 1 &lt; |x| &lt;= 2
    0                for |x| &gt; 2


you can recover a sensible shape.