I am a maya user. I am currently learning Houdini.
I find that the ramp and rainbow vops in the vex editor are not very flexible and controlable compare with the ramp in Maya and 3ds max.(may be I just do not know how to use the ramps in Vex shader)(i was going to use “blendRegions” vop to help me but only 3 regions can be applied!)

Is it posible to import the ramp from COPs (in a procedural way)? Because the ramp in COPs is better than the ramp in vex builder.

A quick search on OdWiki or the forums will reveal the answer to you:
http://odforce.net/wiki/index.php/FrequentlyAskedQuestions [odforce.net]

You'll find a lot of answers out there if you just take a little time to search the forums, the Help and the Wiki.