integral sometimes gives ln with negative aqrgument

Posted on 2008-06-29 18:53 By eyaler (7)

Categories:

How do I ...? with Maple

i do:

int(ln(k3+r)/r^2,r);

i get:

either 1/k3*ln(r)-ln(k3+r)*(k3+r)/k3/r

or 1/k3*ln(-r)-ln(k3+r)*(k3+r)/k3/r

the expected behaviour would be to always get the absolute value inside the ln

logarithms in Maple

Comment on 2008-06-29 19:11 from alec ( Maple Rating 4

1608)

In Maple, numbers are complex by default, and logarithms for negative numbers are defined as log(-n)=log(n)+Pi*I.

with(RealDomain);

would give logarithms of absolute values (but you'll see some other weird things instead.)

Alec

with(RealDomain) does not

Comment on 2008-11-13 06:54 from eyaler (7)

with(RealDomain) does not solve the problem

No solution

Comment on 2008-11-13 21:38 from alec ( Maple Rating 4

1608)

AFAICT, there is no a good solution for working with real numbers in Maple. Just some ad hoc tricks.

Alec

ln and RealDomain

Comment on 2008-11-13 13:23 from jakubi ( Maple Rating 4

943)

For something simpler:

use RealDomain in int(1/x,x) end use;

		ln(x)

Should the output be ln(abs(x)) ? or a piecewise: ln(x) for x>0 and undefined for x<=0 ?

Note, ?RealDomain states:

Results returned by procedures are postprocessed by discarding values containing any detectable non-real answers or replacing them with undefined where appropriate.

there is this

Comment on 2008-11-16 16:08 from edgar ( Maple Rating 2

186)

Re(int(1/x,x));
ln(|x|)

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G A Edgar