Google Groups no longer supports new Usenet posts or subscriptions. Historical content remains viewable.
Dismiss

CPU time for transcendental functions

463 views
Skip to first unread message

Robinn

unread,
Dec 14, 2023, 9:00:13 PM12/14/23
to
I got some old neural network code (written about 30 years ago).
It has several activation functions, which only change 2 lines, like so:

if (activation(1:2).eq.'SI' .or. activation(1:2).eq.'LO') then
output(i,j) = 1.0/(1.0+EXP(-output(i,j))) ! sigmoid
slope(i,j) = output(i,j) * (1.0 - output(i,j)) ! sigmoid
elseif (activation(1:2).eq.'TA') then
output(i,j) = TANH(output(i,j)) ! TANH
slope(i,j) = 1.0 - output(i,j)*output(i,j) ! TANH
elseif (activation(1:2).eq.'AR') then
y = output(i,j)
output(i,j) = ATAN(y) ! arctan
slope(i,j) = 1.0/(1.0 +y*y) ! arctan
elseif (activation(1:5).eq.'SOFTP') then
y = EXP(output(i,j))
output(i,j) = LOG(1.0+y) ! softplus
slope(i,j) = 1.0/(1.0+1.0/y) ! softplus
elseif (activation(1:5).eq.'SOFTS') then
y = output(i,j)
output(i,j) = y/(ABS(y)+1.0) ! softsign
slope(i,j) = 1.0/(1.0+ABS(y))**2 ! softsign

Now when running it, the tanh option is slowest, as expected.
But the sigmoid (using exp) is faster than softsign, which only needs
abs and simple arithmetic. How can this be? Even if exp is using a
table lookup and spline interpolation, I would think that is slower.
Softsign would have an extra divide, but I can't see that tipping the
scales.

Steven G. Kargl

unread,
Dec 14, 2023, 11:22:19 PM12/14/23
to
There is insufficient information to provide much help. First, what
compiler and operating system? Second, how did you do the timing?
Third, is there a minimum working example that others can profile?

--
steve

Giorgio Pastore

unread,
Dec 22, 2023, 9:37:58 AM12/22/23
to
Il 15/12/23 05:22, Steven G. Kargl ha scritto:
Fourth, what were the numbers of timing.

Giorgio

Thomas Jahns

unread,
Jan 30, 2024, 3:40:27 AMJan 30
to
You perhaps are not aware that the string comparisons (for which most compilers
call the strncmp function) you have in your conditionals are quite expensive on
todays CPUs. I would recommend to use an INTEGER constant to make the switch.

Thomas
0 new messages