Why are the effective statements invalid when put them in a proc?

Posted on 2008-08-20 22:50 By math618 (9)

Categories:

How do I ...? with Maple

Hi,the following is my confused problem

the effective statements
   restart;
   with(group):with(StringTools):with(Maplets[Examples]):
   a:=GetInput("Input the moves.");#input: IMIM10IM2IM9IM7IM8IM10
   i:=0:b:=Explode(a):
   M10:=[[2, 12, 7, 4, 11, 6, 10, 8, 9, 5, 3]]:
   M2:=[[2, 5, 8, 6, 4, 12, 3, 9, 10, 11, 7]]:
   M8:=[[2, 4, 10, 5, 12, 11, 8, 3, 7, 6, 9]]:
   M6:=[[2, 6, 3, 11, 5, 4, 9, 7, 8, 12, 10]]:
   M7:=[[2, 11, 9, 12, 6, 5, 7, 10, 3, 4, 8]]:
   M:=[[2, 3, 5, 9, 8, 10, 6, 11, 4, 7, 12]]:
   M9:=[[2, 7, 11, 10, 9, 3, 12, 4, 6, 8, 5]]:
   M3:=[[2, 9, 6, 7, 3, 8, 11, 12, 5, 10, 4]]:
   M4:=[[2, 8, 4, 3, 10, 7, 5, 6, 12, 9, 11]]:
   M5:=[[2, 10, 12, 8, 7, 9, 4, 5, 11, 3, 6]]:
   X:=[[1, 12], [2, 11], [3, 10], [4, 9], [5, 8], [6, 7]]:
   for d in b do
     i:=i+1;
     if d>"0" and d<="9" then i:=i-1;s[i]:=Join(["M",d],"");
       elif d="0" then i:=i-1;s[i]:="M10";
       elif d="I" then s[i]:="X";
       else s[i]:="M";
     end if;
   end do:
   s:=convert(s,list);
   i:=0:for d in convert(s,list) do i:=i+1;s[i]:=convert(s[i],symbol);end do:
   s:=op(s);
   foldl(`mulperms`,s);

but this is invalid!Why?

   restart;
   with(group):with(StringTools):with(Maplets[Examples]):
IM:=proc()
   a:=GetInput("Input the moves.");#input: IMIM10IM2IM9IM7IM8IM10
   i:=0:b:=Explode(a):
   M10:=[[2, 12, 7, 4, 11, 6, 10, 8, 9, 5, 3]]:
   M2:=[[2, 5, 8, 6, 4, 12, 3, 9, 10, 11, 7]]:
   M8:=[[2, 4, 10, 5, 12, 11, 8, 3, 7, 6, 9]]:
   M6:=[[2, 6, 3, 11, 5, 4, 9, 7, 8, 12, 10]]:
   M7:=[[2, 11, 9, 12, 6, 5, 7, 10, 3, 4, 8]]:
   M:=[[2, 3, 5, 9, 8, 10, 6, 11, 4, 7, 12]]:
   M9:=[[2, 7, 11, 10, 9, 3, 12, 4, 6, 8, 5]]:
   M3:=[[2, 9, 6, 7, 3, 8, 11, 12, 5, 10, 4]]:
   M4:=[[2, 8, 4, 3, 10, 7, 5, 6, 12, 9, 11]]:
   M5:=[[2, 10, 12, 8, 7, 9, 4, 5, 11, 3, 6]]:
   X:=[[1, 12], [2, 11], [3, 10], [4, 9], [5, 8], [6, 7]]:
   for d in b do
     i:=i+1;
     if d>"0" and d<="9" then i:=i-1;s[i]:=Join(["M",d],"");
       elif d="0" then i:=i-1;s[i]:="M10";
       elif d="I" then s[i]:="X";
       else s[i]:="M";
     end if;
   end do:
   s:=convert(s,list);
   i:=0:for d in convert(s,list) do i:=i+1;s[i]:=convert(s[i],symbol);end do:
   s:=op(s);
   foldl(`mulperms`,s);
end proc:

I'm sorry.In proc,I forgot

Comment on 2008-08-20 22:59 from math618 (9)

I'm sorry.In proc,I forgot to add "return" before foldl(`mulperms`,s);

not necessary

Comment on 2008-08-20 23:52 from acer ( Maple Rating 4

1377)

The return directive isn't required, for the last statement in the procedure.

acer

suggestions

Comment on 2008-08-21 01:26 from Joe Riel ( Maple Rating 4

1258)

It's generally best if a procedure does not depend on a package having been 'withed'. That is, rather than doing

with(group): with(StringTools): with(Maplets[Examples]):
IM := proc() ... end proc:

you should do

IM := proc()
uses group, StringTools, Maplets:-Examples;
...
end proc:

There appears to be a superfluous convert(s,'list') in the procedure (s was previously converted to a list). Regardless, if I understand what you intend, it is better to do s := map(convert, s, symbol) rather than assigning elements of a list, which is not efficient and only works for relatively small lists (less than 100 elements).

Also, backquotes around foldl serve no useful purpose

there is another problem:the

Comment on 2008-08-27 21:05 from math618 (9)

there is another problem:the symbols in s can not take the corresponding value assigned before!

>   IM:= proc (a::string)
>   uses group, StringTools;
>   local b,d,i,ans,s,M,M2,M3,M4,M5,M6,M7,M8,M9,M10,X;
>
>   i:=0:b:=Explode(a);
>   for d in b do
>     i:=i+1;
>     if d>"0" and d<="9" then i:=i-1;s[i]:=Join(["M",d],"");
>       elif d="0" then i:=i-1;s[i]:="M10";
>       elif d="I" then s[i]:="X";
>       else s[i]:="M";
>     end if;
>   end do:
>   s:=convert(s,list);
>   s:=map(convert, s, symbol);
>   X:=[[1, 12], [2, 11], [3, 10], [4, 9], [5, 8], [6, 7]]:
>   M10:=[[2, 12, 7, 4, 11, 6, 10, 8, 9, 5, 3]]:
>   M2:=[[2, 5, 8, 6, 4, 12, 3, 9, 10, 11, 7]]:
>   M8:=[[2, 4, 10, 5, 12, 11, 8, 3, 7, 6, 9]]:
>   M6:=[[2, 6, 3, 11, 5, 4, 9, 7, 8, 12, 10]]:
>   M7:=[[2, 11, 9, 12, 6, 5, 7, 10, 3, 4, 8]]:
>   M:=[[2, 3, 5, 9, 8, 10, 6, 11, 4, 7, 12]]:
>   M9:=[[2, 7, 11, 10, 9, 3, 12, 4, 6, 8, 5]]:
>   M3:=[[2, 9, 6, 7, 3, 8, 11, 12, 5, 10, 4]]:
>   M4:=[[2, 8, 4, 3, 10, 7, 5, 6, 12, 9, 11]]:
>   M5:=[[2, 10, 12, 8, 7, 9, 4, 5, 11, 3, 6]]:
>   print(X,s[1]);#this output can tell us s[1] cannot take [[1, 12], [2, 11], [3, 10], [4, 9], [5, 8], [6, 7]],why?
>   s:=op(s):
>   foldl(`mulperms`,s);
> end proc:

> IM("IMIM3IM2IM9IM7IM8");
[[1, 12], [2, 11], [3, 10], [4, 9], [5, 8], [6, 7]], X

Error, (in convert/plist) bad index into Array

evaluation

Comment on 2008-08-28 09:57 from Joe Riel ( Maple Rating 4

1258)

There are two related problems, both somewhat subtle, with this routine. First, the Maple procedure convert/symbol returns a global symbol. As such, it will not match the local symbols (variables) in the procedure. A better way to handle this translation is via a table, however, for now let's just use what you have. The simplest change is to redeclare the symbols M, M2, ..., M10, and X to be global. That, alas, does not suffice. The reason is that inside a procedure Maple only evaluates expressions one level. When you do map(convert, s, symbol) the result is a list of symbols, not a list of their values. It is those values which foldl gets and chokes. A work-around for that is to fully evaluate the list, that is add the statement s := eval(s) [before the call to op(s)). With those changes the procedure operates.

As mentioned, a better way to do this is with a table. Create the table

MIX := table(["X" = [[1,12], ...], "M" = [...], ..., "M10" = [...]):

then instead of converting s to symbols, look up the strings in the table

s := [seq([MIX[char], char in s)];

Actually, I'd probably do that inside the loop that parses the individual characters.

That's great!Thank you!

Comment on 2008-08-29 02:04 from math618 (9)

That's great!Thank you!