In Matlab's very old versions, what did "\" stand for in a conditional statement?

For my thesis work I was suggested to use a related code made in year 2000 on Matlab; when transcribing it I found the next syntax for some if loops:

if \ min(x)>= 0
   statement;
end

However it is not valid anymore for recent software's versions. I did some search on Google but using "\" is pretty ambiguous and found nothing out of conditionals. Do you know what does it stand for?