Uninstall any existing gnuplot on your OSX
brew uninstall gnuplot
Install gnuplot with either X or X11
brew-install gnuplot --with-x11
Finally, set the GNUTERM to X11
setenv("GNUTERM","X11")
或者 brew install gnuplot --with-qt
setenv("GNUTERM","qt")
【Machine Learning 学习笔记】OSX Octave 输出图像问题
原文：http://www.cnblogs.com/turtle920/p/5197786.html