> I've just hit an unexpected behavior of the ex.ldegree() method in my

> application. The problem is that ldegree() gives 0 before and 1 (the

> expected value) after calling expand() on the expression. I did not

> expect this, as the tutorial says that degree() and ldegree() "work

> reliably on non-expanded input polynomials".

 

The tutorial is misleading. The only reason why one could claim that [l]degree()

"works reliably" with non-expanded inputs is that the program won't crash.

Proof: try this in ginsh:

 

ldegree(x*(x^2-1) - x^2*(x - 1), x)

 

The code [1] does not expect different terms to cancel each other, hence the problem

 

[1] https://www.ginac.de/ginac.git/?p=ginac.git;a=blob;f=ginac/add.cpp;h=25de6cd2e889555f52aeccae2b263c4ccc2f74a5;hb=refs/heads/master#l279

 

> A small running example and its output are attached. The expression is

> the one I encountered in my application. This looks like a bug to me, or

> is it necessary to call expand() before using ldegree()?

 

One should expand the expression before using degree(), ldegree(), coeff()

 

Best regards,

Alexey