How can I set the refresh rate

Hi everyone,

My monitor is 38402160, and the output is miniDP. I want to convert the output to HDMI. But the monitor says there is no input. Then I set the resolution to 38402160_30 by nvidia-settings. It really works. I also clicked ‘Save to Configuration File’.

But after rebooting, there still no input.

I try to use ‘sudo xrandr --addmode DP-3 3840×2160_30.00’. But there are some errors such as X Error of failed request: BadMatch (invalid parameter attributes).

The operate system is Ubuntu 16.04.

Did somebody encounter this problem?
Could someone give me some solutions or advices?

Thanks in advance.