(maxima.info)Package facexp

---

Next: Package functs Prev: Package absimp Up: simplification-pkg

---

Enter node , (file) or (file)node

81.3 Package facexp
===================

The 'facexp' package contains several related functions that provide the
user with the ability to structure expressions by controlled expansion.
This capability is especially useful when the expression contains
variables that have physical meaning, because it is often true that the
most economical form of such an expression can be obtained by fully
expanding the expression with respect to those variables, and then
factoring their coefficients.  While it is true that this procedure is
not difficult to carry out using standard Maxima functions, additional
fine-tuning may also be desirable, and these finishing touches can be
more difficult to apply.

   The function 'facsum' and its related forms provide a convenient
means for controlling the structure of expressions in this way.  Another
function, 'collectterms', can be used to add two or more expressions
that have already been simplified to this form, without resimplifying
the whole expression again.  This function may be useful when the
expressions are very large.

   'load ("facexp")' loads this package.  'demo ("facexp")' shows a
demonstration of this package.

 -- Function: facsum (<expr>, <arg_1>, ..., <arg_n>)
     Returns a form of <expr> which depends on the arguments <arg_1>,
     ..., <arg_n>.  The arguments can be any form suitable for
     'ratvars', or they can be lists of such forms.  If the arguments
     are not lists, then the form returned is fully expanded with
     respect to the arguments, and the coefficients of the arguments are
     factored.  These coefficients are free of the arguments, except
     perhaps in a non-rational sense.

     If any of the arguments are lists, then all such lists are combined
     into a single list, and instead of calling 'factor' on the
     coefficients of the arguments, 'facsum' calls itself on these
     coefficients, using this newly constructed single list as the new
     argument list for this recursive call.  This process can be
     repeated to arbitrary depth by nesting the desired elements in
     lists.

     It is possible that one may wish to 'facsum' with respect to more
     complicated subexpressions, such as 'log (x + y)'.  Such arguments
     are also permissible.

     Occasionally the user may wish to obtain any of the above forms for
     expressions which are specified only by their leading operators.
     For example, one may wish to 'facsum' with respect to all 'log''s.
     In this situation, one may include among the arguments either the
     specific 'log''s which are to be treated in this way, or
     alternatively, either the expression 'operator (log)' or ''operator
     (log)'.  If one wished to 'facsum' the expression <expr> with
     respect to the operators <op_1>, ..., <op_n>, one would evaluate
     'facsum (<expr>, operator (<op_1>, ..., <op_n>))'.  The 'operator'
     form may also appear inside list arguments.

     In addition, the setting of the switches 'facsum_combine' and
     'nextlayerfactor' may affect the result of 'facsum'.

 -- Global variable: nextlayerfactor
     Default value: 'false'

     When 'nextlayerfactor' is 'true', recursive calls of 'facsum' are
     applied to the factors of the factored form of the coefficients of
     the arguments.

     When 'false', 'facsum' is applied to each coefficient as a whole
     whenever recusive calls to 'facsum' occur.

     Inclusion of the atom 'nextlayerfactor' in the argument list of
     'facsum' has the effect of 'nextlayerfactor: true', but for the
     next level of the expression only.  Since 'nextlayerfactor' is
     always bound to either 'true' or 'false', it must be presented
     single-quoted whenever it appears in the argument list of 'facsum'.

 -- Global variable: facsum_combine
     Default value: 'true'

     'facsum_combine' controls the form of the final result returned by
     'facsum' when its argument is a quotient of polynomials.  If
     'facsum_combine' is 'false' then the form will be returned as a
     fully expanded sum as described above, but if 'true', then the
     expression returned is a ratio of polynomials, with each polynomial
     in the form described above.

     The 'true' setting of this switch is useful when one wants to
     'facsum' both the numerator and denominator of a rational
     expression, but does not want the denominator to be multiplied
     through the terms of the numerator.

 -- Function: factorfacsum (<expr>, <arg_1>, ... <arg_n>)
     Returns a form of <expr> which is obtained by calling 'facsum' on
     the factors of <expr> with <arg_1>, ...  <arg_n> as arguments.  If
     any of the factors of <expr> is raised to a power, both the factor
     and the exponent will be processed in this way.

 -- Function: collectterms (<expr>, <arg_1>, ..., <arg_n>)

     Collects all terms that contain <arg_1> ...  <arg_n>.  If several
     expressions have been simplified with the following functions
     'facsum', 'factorfacsum', 'factenexpand', 'facexpten' or
     'factorfacexpten', and they are to be added together, it may be
     desirable to combine them using the function 'collecterms'.
     'collecterms' can take as arguments all of the arguments that can
     be given to these other associated functions with the exception of
     'nextlayerfactor', which has no effect on 'collectterms'.  The
     advantage of 'collectterms' is that it returns a form similar to
     'facsum', but since it is adding forms that have already been
     processed by 'facsum', it does not need to repeat that effort.
     This capability is especially useful when the expressions to be
     summed are very large.

     See also 'factor'.

     Example:

          (%i1) (exp(x)+2)*x+exp(x);
                                       x          x
          (%o1)                   x (%e  + 2) + %e
          (%i2) collectterms(expand(%),exp(x));
                                            x
          (%o2)                   (x + 1) %e  + 2 x