Dear friends:
I downloaded the C++ Mathematical Expression Library from the web, and i uploaded  it in the attachment. 
 It consists of only one head file.  But the compiling process is very slow under opensuse 42.3 with gcc. Could you please give me some advices for that.
   Regards.

The web is huge. No one can guess what you downloaded or what site. Try again, don't leave out details and as to slow compiling I'm finding new coders that complain when compiles take a minute. They freak when we show them how long it takes to compile a Linux distro.

Nothing wrong with a compile taking time, is there?

commented: Nope! +15

On my 8 core CentOS server, it takes over an hour to compile a complete kernel - that just uses one core. If I add the "-j number-of-jobs" option to make such as "make -j 4" it will use 4 cores and takes about 15 minutes to build. I usually only use 4 jobs since building the kernel is a background process and I have enough power left over to continue with other work.

commented: Nice to read as it's a reminder how to enable more cores for the make/compile. +12

I am sorry i forgoten uploading the source file

We don't need the source file, but a link to the site where you found that library.