@Markiyan Hirnyk It would be useful, as a first step to the 3D goal, to have a canonical ordering of the vertices, edges, or faces of polyhedra.

Please re-run the command without the 'evaluate' option and post the results. If the code contains large matrices, please reduce them to 2x2 examples.

 Your initial conditions contain

ur(e,0)=1/ch(e)

What is ch? Do you mean cosh? 

If I change it to cosh, I still get an error, but it's a different error with a more-informative message. But I am not pursuing that error any further unless you say that cosh(e) is what you meant.

@emma hassan Sorry, I don't know enough about finite difference solutions to PDEs to help you anymore with this.

@emma hassan Sorry, I don't know enough about finite difference solutions to PDEs to help you anymore with this.

@Alejandro Jakubi 

Is that replacement of the print/foo mechanism by a "PrintTools" package an expresion of desire or work in progress?

It may not be fair or polite to ask the scientists, in a public forum, about works in progress. They may be contracturally required to give no answer either way, and then they feel bad for seeming impolite by ignoring you.

@User716 In my opinion, one usually finds that eval is ultimately easier to use than assign in most cases, even though assign often initially seems to be the easier one. This is even more true in a loop.

@User716 In my opinion, one usually finds that eval is ultimately easier to use than assign in most cases, even though assign often initially seems to be the easier one. This is even more true in a loop.

@emma hassan Make i= 0..M. If I do this, it runs fine, and I get a list of purely numeric points.

@emma hassan Make i= 0..M. If I do this, it runs fine, and I get a list of purely numeric points.

@emma hassan The worksheet that you attached to the most recent reply is slightly different from the one that you attached to your previous reply. The latter has the line

whereas the former has the line

You need to have the range of i= 0..M.

@emma hassan The worksheet that you attached to the most recent reply is slightly different from the one that you attached to your previous reply. The latter has the line

whereas the former has the line

You need to have the range of i= 0..M.

@adel-00 Of course your higher-degree polynomial can be solved; it is already factored into factors of degree less than 5. Finding the roots of a polynomial is only as hard as finding the roots of the factors. Your first polynomial cannot be solved exactly even for the simple case b=1, k=1, so how can it be solved for arbitrary b and k?

@wrestler04 Remember, that should be exp(-10*x), not exp^(-10*x). Let me know if that works for you.

On the one hand, it seems that you want tend to go from 0 to 12; and on the other hand, it seems that you want it to go from 0 to 50. You can't do both at the same time! Obviously, you know that; so I have to ask you to describe more precisely what you are trying to achieve.

Side note: You need to set the value of alpha. That problem won't manifest until you fix the tend problem.