What does this icon mean when parallel computation is using?

What does this icon in the lower left corner of the Matlab window mean, when parallel computation is using?

I found when I did not use parallel computation this four-column icon is grey, like inactive mode. When I was using parallel computation, sometims it was blue four-column icon; sometims it was green four-column icon; sometims it was green two-column icon. What does the number of columns and color of this icon means?

Answer 1

[Sean de Wolski]

The amount of green columns is trying to show the current utilization of the workers in the parallel pool.

If you have 16 workers and run a parfor loop from 1:4, it should show 1 green bar.

[Devin]

How about the blue four-column icon?

[Walter Roberson]

Blue four-column is four inactive workers. 4 workers, 4 bars.

[Sean de Wolski]

There's always four blue bars to show the pool as open, even with two workers or 64. Apparently that's what the icon design folks liked. My guess is that two blue bars is reserved for the pause button.