how do I use compute_cartesian_path function?

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when I use compute_cartesian_path , I often get erorr. the value of fraction is 89%,32%,50% etc. I try to give long time and more tempt to IK . It is not good, I will get strange trajectory. I get waypoints in RVIZ using commander of "current". I doubt that I make mistake in here.

I want to know how can I get correct waypoints?and how do I use compute_cartesian_path function?

I have other question whether the compute_cartesian_path is used in two arms.