Clarify that Polyratfun numerator expansion is relative

[benruijl]

When all terms in the numerator depend on the expansion variable and have power > 1, polyratfun(expand,....) does not truncate the numerator.

S eps;
CF rat;
Polyratfun rat(expand,eps,3);

L F = rat(eps^4,1);
Print +s;
.end

Gives rat(eps^4,1) instead of rat(1,1).

Similary, it will not expand rat(eps^4 + eps^5,1); and rat(eps^2 + eps^5,1); It will expand rat(eps + eps^5,1); and rat(1 + eps^5,1);.

This is in contradiction with the manual, where it says: "eventually all terms with powers of x that are greater than ’power’ will be discarded".

[vermaseren]

Don’t forget that the expansion is relative to the leading term. You can try rat(ep^4+ep^5+ep^6+ep^7+ep^8,1) and see what happens.

Jos

On 8 Jun 2020, at 14:41, Ben Ruijl notifications@github.com wrote:

When all terms in the numerator depend on the expansion variable and have power > 1, polyratfun(expand,....) does not truncate the numerator.

S eps; CF rat; Polyratfun rat(expand,eps,3);

L F = rat(eps^4,1); Print +s; .end Gives rat(eps^4,1) instead of rat(1,1).

Similary, it will not expand rat(eps^4 + eps^5,1); and rat(eps^2 + eps^5,1); It will expand rat(eps + eps^5,1); and rat(1 + eps^5,1);.

This is in contradiction with the manual, where it says: "eventually all terms with powers of x that are greater than ’power’ will be discarded".

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[benruijl]

I figured something like this is happening, but then we should write that in the manual more clearly.

I interpret "eventually all terms with powers of x that are greater than ’power’ will be discarded" as a statement about the absolute power of x.