@acer I tested the code you give me in the link.It does not generate graphs.In the Fourth line,I correct _i to I,so P1 can be generated.But P2 fails,and the code is somehow diffcult to read,or beyond my extend.

 I do not know how to construct the whole thing.My curve is constructed with "intersection" command,it can not be expressed in z=f(x,y),so I can not use plot3d or spacecurve command.That is disturbing.

@acer Maybe it is the reason.But the second graph works well,so I guess maybe it does have the ablity to change the color of spacecurve

@Joe Riel Thank you.I now know it is a bug.

Also I find that after I saved the file,the next time I open the file,the probe quantities is not the same with the original. Shown in picture.What's wrong?

first time

 second time

Thank you for your reply.The file in the picture has being deleted,as I have tried and failed many times,made many files.

So this morning I follow the user guide and try again and the same issue occurs,shown below.The quantities selected in Probe1 are not the same with yesterday's picture,but it doesn't matter.

I upload three files.The first is I follow the user guide,and make it.The second is the standard example,and works well.the third is modified standard example,What I do is just delete the probe,attaching a probe at the same place , selecting same quantities to measure.The error message is same.

Thanks for taking your time!

未命名3.msim

Analysis_of_Simple_Hydraulic_Network.msim

Modified_Analysis_of_Simple_Hydraulic_Network.msim

Thanks,I get it!

to be explicit,do the convolution integral