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Math-NumSeq-45
River stage zero No dependents
3 ++
/ Math::NumSeq::Expression

NAME

Math::NumSeq::Expression -- mathematical expression values

SYNOPSIS

 use Math::NumSeq::Expression;
 my $seq = Math::NumSeq::Expression->new (expression => '2*i+1');
 my ($i, $value) = $seq->next;

DESCRIPTION

A string expression evaluated at i=0, 1, 2, etc, by Perl or a choice of evaluator modules.

This is designed to take expression strings from user input though could be used for something quick from program code too.

Perl

The default expression_evaluator => 'Perl' evaluates with Perl itself. This is always available. Expressions are run with the Safe module to restrict to arithmetic (see Safe).

The i index is in a $i variable and an i() function. The i() function is prototyped like a constant.

    i+1
    2*$i - 2

The functions made available include

    atan2 sin cos exp log                 \    Perl builtins
      sqrt rand                           /
    min max                               List::Util
    floor ceil                            POSIX module
    cbrt hypot erf erfc expm1             \
      j0 j1 jn lgamma_r log10              |  Math::Libm
      log1p pow rint y0 y1 yn             /
    tan asin acos atan                    \
      csc cosec sec cot cotan              |  Math::Trig
      acsc acosec asec acot acotan         |
      sinh cosh tanh                       |
      csch cosech sech coth cotanh         |
      asinh acosh atanh                    |
      acsch acosech asech acoth acotanh   /

Math-Symbolic

expression_evaluator => 'MS' selects the Math::Symbolic module, if available.

The expression is parsed with Math::Symbolic->parse_from_string() and should use a single variable for the i index in the sequence. The variable can be any name, not just "i"

    2*i+1
    x^2 + x + 1           # any single variable

The usual $ms->simplify() is applied to perhaps reduce the expression a bit, then to_sub() for actual evaluation.

Math-Expression-Evaluator

expression_evaluator => 'MEE' selects the Math::Expression::Evaluator module, if available.

The expression should use a single input variable, which can be any name, and takes the i index in the sequence. Temporary variables can be used by assigning to them,

    x^2 + x + 1      # any single variable
    t=2*i; t^2       # temporary variables assigned

The expression is run with $mee->compiled(). It turns the expression into a Perl subr for actual evaluation.

Language-Expr

expression_evaluator => 'LE' selects the Language::Expr module, if available.

The expression should use a single variable, of any name, which will be the i index in the sequence. See Language::Expr::Manual::Syntax for the expression syntax.

    $x*$x + $x + 1

The expression is compiled with Language::Expr::Compiler::Perl for evaluation.

FUNCTIONS

See "FUNCTIONS" in Math::NumSeq for behaviour common to all sequence classes.

$seq = Math::NumSeq::Expression->new (radix => $r, modulus => $d)

Create and return a new sequence object.

$value = $seq->ith($i)

Return the expression evaluated at $i.

BUGS

Safe.pm seems a bit of a slowdown. Is that right or is it supposed to validate ops during the eval which compiles a subr?

SEE ALSO

Math::NumSeq

HOME PAGE

http://user42.tuxfamily.org/math-numseq/index.html

LICENSE

Copyright 2010, 2011, 2012 Kevin Ryde

Math-NumSeq is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.

Math-NumSeq is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with Math-NumSeq. If not, see <http://www.gnu.org/licenses/>.