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Plot problem with function

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From	"I.N. Galidakis" <morpheus@olympus.mons>
Newsgroups	comp.soft-sys.math.maple
Subject	Plot problem with function
Date	Thu, 28 Jul 2011 22:09:38 +0300
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I am having some problems with Maple 9 when plotting a certain function. The 
function is:

> HW:=proc()
> local y,n,c,s,p,sol,i,aprx,dy,dist,r,oldr,newr,fun,dfun,eps;
> if nargs<2 then ERROR("At least two arguments required.") fi;
> n:= args[-1];y:=args[-2];c:= [args[1..-3]];
> if y=0 then 0 else
>  dist:=infinity;
>  eps:=1e-32;
>  fun:= 1;
>  for i from 1 to nargs-2 do fun:= exp(c[i]*fun) od;
>  fun:= z*fun-y;
>  dfun:=diff(fun,z);
>  s:=series(fun,z,n);
>  p:=convert(s,polynom);
>  sol:={fsolve(p=0,z,complex)}; #complex?
>  for i from 1 to nops(sol) do
>   aprx:=evalf(subs(z=op(i,sol),fun));
>   dy:=evalf(abs(aprx));
>   if dy<=dist then r:=op(i,sol);dist:=dy;fi;
>  od;
> #start Newton with approximate zero found.
>  oldr:=r;
>  newr:=r-evalf(subs(z=r,fun)/subs(z=r,dfun));
>  for i from 1 to 1000 while (abs((oldr-newr)/oldr)>eps) do
>   oldr:=newr;
>   newr:=newr-evalf(subs(z=newr,fun)/subs(z=newr,dfun));
>  od;
> newr;
> fi;
> end:

When I try to plot it (in this case the arguments make it equivalent to arcsin) 
I get:

> with(plots):
> plot(HW(log(sin(z)/z),y,10),y=-1..1);
Error, (in fsolve) y is in the equation, and is not solved for

while if I do a:

> N:=50;x1:=-1;x2:=1;
> x:=n->x1+abs(x2-x1)/N*n;
> L:=[seq([x(n),HW(log(sin(z)/z),x(n),10)],n=0..N)]:
> plot(L,scaling=constrained);

It works (shows the graph of arcsin).

Individual values seem to be calculated correctly. For example:

> HW(log(sin(z)/z),0.245,10);
.247519692533815916885429116210

Does anyone know why the plot command doesn't work with this function?

Many thanks,
--
I.

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Thread

Plot problem with function "I.N. Galidakis" <morpheus@olympus.mons> - 2011-07-28 22:09 +0300
  Re: Plot problem with function Joe Riel <joer@san.rr.com> - 2011-07-28 12:18 -0700
    Re: Plot problem with function "I.N. Galidakis" <morpheus@olympus.mons> - 2011-07-29 00:11 +0300
      Re: Plot problem with function Joe Riel <joer@san.rr.com> - 2011-07-28 14:31 -0700

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