@Pascal4QM Thank you so much for solving my problem!

@tomleslie Thank you for pointing out my error.

@Carl Love You write a detailed solution to help me solve the problem. Thank you!

@vv I like this function so much!I think it should be included in maple

@Carl Love Thank you! I get it.

@vv  @Carl Love gives a traditional definition of limit and I am accustomed to it.You say limit point is a cluster point(=accumulation point),I am somehow puzzled.Cluster point allow the neighbourhood near zero to have undefined points,while limit's tradition defition require all points in the neighbour have defition(if I does not get it wrong).So I want to see your reference of definition of limit to judge which is right.(plus:I scan the wiki but can not find this definition)

@Carl Love However, for function sin(sin(x)/x)/(sin(x)/x) ,the function does not have definition at points x=n*Pi,

n belongs to integer.So There is numourous undefined points in the domain (c,infinity),c is a real number.

@acer Thank you for your help.

@acer  I tried but it does not work

@Carl Love COLOR option can be a good alternative to colorscheme.Thank you for your effort!

@acer You give me an awsome example.I will follow it.

@Carl Love Hello,I find that colorscheme do not work even on tubeplot,whether I use colorscheme= ["xyzcoloring",(x,y,z)->'*'] or colorscheme= ["xyzcoloring", `+`],or colorscheme= ["xyzcoloring",(x,y,z)->x+y+z] ,colorscheme= ["xyzcoloring",(x,y,z)->x*y*z], the color of the tube does not change.

@acer Thank you.Show me at your spare time.

@Kitonum Thank you for broaden my horizon.I will study how matrix can be used to parameterize the equation.

@Carl Love I get it.I will study the usage of the elimilate command and the way you parameterize the spacecurve.Thank you!