Q: how can i connect my iphone 4 with my ipad retina by bluetooth???

The Bluetooth on iPad is meant for earplug, headset, keyboard, car hands-free set and speakers.

iOS: Understanding Personal Hotspot

http://support.apple.com/kb/HT4517

Use Bluetooth to tether your iPhone, iPod touch, or iPad

http://www.macworld.com/article/1159258/bluetooth_tethering.html

How to Connect an iPad to an iPhone Via Bluetooth Tethering

http://techtips.salon.com/connect-ipad-iphone-via-bluetooth-tethering-25472.html

Tethering an iPad to an Android Cell Phone

http://everydaylife.globalpost.com/tethering-ipad-android-cell-phone-33675.html

How to Reconnect a Forgotten Bluetooth Device on an iPad

http://techchannel.radioshack.com/reconnect-forgotten-bluetooth-device-ipad-1037 .html

 Cheers, Tom

As Diavonex explained, Bluetooth on an iPad is used to connect speakers, headphones, keyboards and a few other things. It is not set up to connect two iOS devices. Perhaps if you explained what you want to accomplish with the connection we can help you learn how to do it.