@Joe Riel Thank you for explainng that.

@mmcdara

In fact I would be happy with [123,0,321]; they are data points in range 0 to 1000.

I am still curious why convert("531",integer) gives that error message.

Origin of problem: I generated a long list of 3 digit numbers that I wanted to plot. However, I did not notice that there were no spaces or commas betwen the entires. I was trying to salvage all that typing.

I tried these simple procedures that fail and I was curious about Maple's pattern matching capabilities. (I think this would be very simple in Mathematica.)

f:=proc (x) if x= "y" then y end if end proc;
or

f:=proc (x:: "y")  y  end proc;
 

@dharr 

Since h(0,x) =diff(f(u,x),x) at  u = 0 and f(0,x) = g then h(0,x) must be diff(g,x) to be consistent. I should have mentioned that I tried that for another dead end. Here is the message:

Error, (in pdsolve/numeric/match_PDEs_BCs) cannot handle systems with multiple PDE describing the time dependence of the same dependent variable, or having no time dependence

@Preben Alsholm Hi,

Thankk you for your response.

I checked kernelopts(floatPi); in both Maple 2019 and 2020 and got true in both cases.

However, I realized from your answer that I got the wrong answer when Digits was set to 10 but if I put Digits:=15 all was well. I guess I was seeing round off error.

@Carl Love  That is quite subtle. Good to know. Thank you. I guess the longer displayprecision

is the command I will have to use.

@acer 

Thank you for explaining my error. As Tom Leslie also pointed out using evalf( ....,5) was my problem.

From the syntax-it sure looks like a composition- I assumed that since  f(g(x)) is computed by first computing g(x) then applying f to that result evalf( eval([W,Wp],nans(1.5)),5) would be computed by first evaluating eval([W,Wp],nans(1.5)), then applying evalf..., 5) to that answer.

In my work I was using dsolve with Digits:=35 and error tolerances of 10 ^(-14). I guess evalf overrides those instructions somehow. So be it.

The interface setting does resolve my issue.

@tomleslie 

I do not see any major changes you have made. Could you please explain? I also do not understand what you dislike about my code or where it might go wrong. f'^2 cos(x) /f^2 > 0 for any any f if 0 < x < πi/2.

@Carl Love evalf_error.pdf

does this help?

evalf_error_3.mw
 

@Earl  I am hoping that the full set of rules for using events will appear-perhaps inMaple 2021-and will answer all my questions. Meanwhile, it is useful to see your apllication of the command.

@Preben Alsholm 

Thanks.

So I am not the only one who finds the Help pages opaque.

BTW, I still rely on an answer you suplplied 9?15/17 to use events. I am hoping to be able to use the commands more comfortably in Maple 2021.
 

@Kitonum I just have to remember it. Wouldn't it be nice if it was one of the examples on the Help page?

@acer 
Thank you for clarifying the syntax.
I am familiar with the archaic usuage of the dot to denote concatenation but that was not my intent; I was merely eliminating spaces and hoping that would be more acceptable to Maple.

@acer 

Thanks for your help. The 2D supresses y(x) but not dy(x)/dx.