Error in t-SNE momentum gain calculation

[andrewdalpino]

The computation of the gains for t-SNE Gradient Descent with momentum updates is backwards. Instead of speeding up when the gradient is sloping down, it slows down and vice versa. The effect is slower embedding and clusters that are too close together. Just flip the comparison to less than instead of greater than and boom.

 $gain = $direction[$i][$j] < 0.
     ? $gain + self::INC_GAIN
     : $gain * self::DEC_GAIN;