undefined variable "mr" or undefined class "mr.opts"

[ZhaoieeUCAS]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'E:\MRF\mrf-master\mrf'
2. Click on 'Run'
3. See error :
   undefined variable "mr" or class"mr.opts"。

error: gen_MRF_sequence_pulseq (line 27)
system = mr.opts('MaxGrad',Gmax,'GradUnit','mT/m',...

error: demo_MRF (line 7)
[kshot, dcf, ind, TR_all, FA_all, TE_all] = gen_MRF_sequence_pulseq();

where can I find the declaration of the class "mr"