type conversion

[Ulf Kuehn <kuehn@math.uni-hamburg.de>]

hi,
in some computations i generate generic variables, say a_1, a_2, ...,
which for a later use within parallel computations should become local variables.
how to realize this possible in pari (using eval unfortunally doesn't work)

? my(eval(Str("a_",1)))
  ***   variable name expected: my(eval(Str("a_",1)))
  ***                              ^------------------
?

the evaluation of a very large polynomial pol by using  "substvec( pol, [ variables], [values / or new variables] ) "
takes very, very long. experiments show that the evaluation of a polynomial function  " (variables) -> pol " 
is much faster. so my second question is how to convert efficiently a polynomial into a function

? f=a*b;
? g=(a,b) -> f;
? g(x,y)
%15 = b*a
? g=(a,b) -> eval(f);
? g(x,y)
%17 = y*x
?

using "eval"  works if there are no side relations, however if there side relations, these are all contained  in "eval(f)" as a long list
"(a,b) -> my(  list of all relations  from the program ); a*b ;"

best regards,
ulf

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