alpha blending in parallel coordinate plot

[dicook]

this should be put on a nonlinear scale like the scatterplot - it takes too long holding the - key down before the lines clearly become transparent. using the pollen data example.

[hadley]

We should probably do a little thinking about what this curve should look like? Maybe something logistic?

[dicook]

i don't think its too complicated. eyes see in a log function, so an exponential function is all that is needed. it works very nicely - look at the scatterplot and density plot

[yihui]

this has been fixed temporarily