Re: MuPAD 3.0 and collect

Brad Cooper wrote:

If    map(%, map, collect, `ρ`*sin(`θ`));    is what the user
is trying to achieve, but does the steps one at a time...

map(%, map, collect, `ρ`);
map(%, map, collect, sin(`θ`));

Or map(%, map, collect, [`ρ`, sin(`θ`)]), for yet another result.

vice-versa. This means the intended collection where  `ρ` and
sin(`θ`))
are together, will not be achieved. To overcome this, the user has to
carefully
go through all the operands and exclude some of them from the collection.

If (and I realize this is a big if) the `ρ`*sin(`θ`) are already in a product (no distributive law required etc.), you can use

subs(collect(subsex(ex1, `ρ`*sin(`θ`)=tmp), tmp),
     tmp=`ρ`*sin(`θ`))

The same holds for 1/r.

This approach is, unfortunately, not a sufficient way of implementing a better collect function, simply because of the limitations expressed above.

I realise the difficulty of even the "simple" case of collect(obj, 1/r)
recognising (x/r+1/r) as a hit.

That one actually is pretty simple, since MuPAD represents x/r as x*r^-1. collect uses polynomial arithmetic and poly does not accept 1/r as indeterminate.


But I agree that products and 1/r should work, too.


Do you want me to report this as a bug?

That would be a good idea, since I won't have time to look into this in the near future.


regards,
	Christopher
.

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