# Is there any function can compute the value of sgn?

58 views (last 30 days)
Sarah A on 8 Aug 2018
Commented: Star Strider on 9 Aug 2018
Hello,
I read in a paper the following : sgn(A.B), where A and B are vectors. So what does that mean and is there any built in function that can do that? note that sgn is the sigmoid.
Regards,

Star Strider on 8 Aug 2018
The closest you can lkikely get is the sigmf (link) function in the Fuzzy Logic Toolbox.
You can easily write your own:
sgn = @(x,a,c) 1./(1 + exp(-a.*(x-c))); % Create Function
x = 0:0.1:10;
y = sgn(x, 2, 4);
plot(x,y)
xlabel('sigmf, P = [2 4]')
ylim([-0.05 1.05])
This plot matches the one in the documentation.
Experiment to get the result you want.

Sarah A on 9 Aug 2018
Thank you for your answer. could you please explain to me what are a and c ?
Star Strider on 9 Aug 2018
As always, my pleasure.
They are scaling constants for the membership function.
This may not be the version you want, however. If you have a description of your function and the arguments, and the context in which you are using it, we can get closer to creating it. There appear to be several versions of the sigmoid function.