Re: [fricas-devel] Giving a name to a part of an expression
Maybe this would help: http://axiom-wiki.newsynthesis.org/ManipulatingExpressions On Mon, Oct 1, 2018 at 2:01 PM Slawomir Kolodynski wrote: > > Thank you for looking into this. > > >Instead, various routines analyze structure of expressions using lower level > >operations. > > Could you give some examples of those lower level operations? Pattern > matching and rewrite rules seem very useful to me , but I am ok with doing > lower level operations if those fail. I know about numerator, denominator and > monomials so for example I can do > > e1 := (y-m)*x/s > (monomials numerator e1)(1) > > to get x*y > > However when I try to do something similar with > > e2 := (y-m)*sqrt(x)/s > numerator e2 > > to get (y-m)*sqrt(x), I don't know how then to extract the components of this > product. Also, I could not find a way to extract an argument of a function, > for example if I have an expression > > sin(a*x+b) > > how to get the "a*x+b" part? > Thanks, > > Slawomir > -- You received this message because you are subscribed to the Google Groups "FriCAS - computer algebra system" group. To unsubscribe from this group and stop receiving emails from it, send an email to fricas-devel+unsubscr...@googlegroups.com. To post to this group, send email to fricas-devel@googlegroups.com. Visit this group at https://groups.google.com/group/fricas-devel. For more options, visit https://groups.google.com/d/optout.
Re: [fricas-devel] Giving a name to a part of an expression
Thank you for looking into this. >Instead, various routines analyze structure of expressions using lower level operations. Could you give some examples of those lower level operations? Pattern matching and rewrite rules seem very useful to me , but I am ok with doing lower level operations if those fail. I know about numerator, denominator and monomials so for example I can do e1 := (y-m)*x/s (monomials numerator e1)(1) to get x*y However when I try to do something similar with e2 := (y-m)*sqrt(x)/s numerator e2 to get (y-m)*sqrt(x), I don't know how then to extract the components of this product. Also, I could not find a way to extract an argument of a function, for example if I have an expression sin(a*x+b) how to get the "a*x+b" part? Thanks, Slawomir -- You received this message because you are subscribed to the Google Groups "FriCAS - computer algebra system" group. To unsubscribe from this group and stop receiving emails from it, send an email to fricas-devel+unsubscr...@googlegroups.com. To post to this group, send email to fricas-devel@googlegroups.com. Visit this group at https://groups.google.com/group/fricas-devel. For more options, visit https://groups.google.com/d/optout.
Re: [fricas-devel] Giving a name to a part of an expression
I wrote:
>
> Slawomir Kolodynski wrote:
> >
> > Suppose I have an expression like *(y-m)*sqrt(x)/s* . What I would like to
> > do is to give a name *e* to the *sqrt(x)/s* part and do some kind of
> > transformation on this expression so that I get *(y-m)*e *or equivalent as
> > the result*. *To do that I define a rule
> >
> > substE := rule (('y-'m)*sqrt('x)/'s == ('y-'m)*'e)
> >
> > However, when I try to apply this rule to the expression
> >
> > substE (y-m)*sqrt(x)/s
> >
> > I get the *(y-m)*sqrt(x)/s *expression back instead of *(y-m)*e. *It looks
> > like the left hand side of the equality in the rule substE does not pattern
> > match itself.
>
> Yes. In expression numerator is a sum, that is what you really
> have is:
>
> y*sqrt(x) - m*sqrt(x)
>
> In pattern (to which left hand side of the rule is converted) we
> have product. Product does not match sum... I need to check
> is this is just a bug or an unavoidable misfeature.
AFAICS the problem is in convertion from polynomials to patterns.
Looks like a bug, but attempting to fix it showed other
problems with rules, so I need to dig deeper.
--
Waldek Hebisch
--
You received this message because you are subscribed to the Google Groups
"FriCAS - computer algebra system" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to fricas-devel+unsubscr...@googlegroups.com.
To post to this group, send email to fricas-devel@googlegroups.com.
Visit this group at https://groups.google.com/group/fricas-devel.
For more options, visit https://groups.google.com/d/optout.
