nl_tokens: Calculate the slopes of the tangents ( Hermite - type interpolation ) based on the following paper : Steffen M . 1990 . A Simple Method for Monotonic Interpolation in One Dimension . Astronomy and Astrophysics Vol . 239 NO . NOV ( II ) P . 443 1990 .
pl_tokens: function slope3 ( that , x2 , y2 ) { var h0 = that . _x1 - that . _x0 , h1 = x2 - that . _x1 , s0 = ( that . _y1 - that . _y0 ) / ( h0 || h1 < 0 && - 0 ) , s1 = ( y2 - that . _y1 ) / ( h1 || h0 < 0 && - 0 ) , p = ( s0 * h1 + s1 * h0 ) / ( h0 + h1 ) ; return ( sign ( s0 ) + sign ( s1 ) ) * Math . min ( Math . <mask> ( s0 ) , Math . abs ( s1 ) , 0.5 * Math . abs ( p ) ) || 0 ; }