realmax is really real max, but is realmin really real min?

Question

the cyclist 2015-11-2

评论： the cyclist 2015-11-2

The following is expected behavior for realmax:

>> realmax
ans = 
1.797693134862316e+308
>> realmax*2
ans = 
Inf

But the following is unexpected behavior for realmin (at least for me):

>> realmin
ans = 
2.225073858507201e-308
>> realmin/2
ans = 
1.112536929253601e-308

I keep getting representable numbers until I divide realmin by 2^53. Am I missing a subtlety in what "realmin" means?

Answer 1

Mike Garrity 2015-11-2

I think that you're seeing the denorms. They allow you to get closer to 0, but at the cost of a significant dropoff in precision and performance.

the cyclist 2015-11-2

Ah. Today I learned about subnormal numbers, and gradual underflow. Very interesting. Thanks!