On Thu, Feb 26, 2015 at 4:05 PM, Paul Royik <[email protected]> wrote:
> It doesn't work if x is positive.
Indeed, looks like a bug. As a workaround, you can always substitute
general "x" for the positive "x", then it will work:
In [4]: x = Symbol("x", positive=True)
In [5]: powsimp(sqrt(x)*sqrt(x-4), force=True)
Out[5]:
___ _______
╲╱ x ⋅╲╱ x - 4
In [6]: powsimp((sqrt(x)*sqrt(x-4)).subs(x, Symbol("x"), force=True)
...:
KeyboardInterrupt
In [6]: powsimp((sqrt(x)*sqrt(x-4)).subs(x, Symbol("x")), force=True)
Out[6]:
___________
╲╱ x⋅(x - 4)
> In fact, when x is positive, 1/sqrt(x*(x-4)) automatically converted to
> 1/sqrt(x)/sqrt(x-4)
The same trick:
In [7]: powsimp(1/(sqrt(x)*sqrt(x-4)).subs(x, Symbol("x")), force=True)
Out[7]:
1
─────────────
___________
╲╱ x⋅(x - 4)
Ondrej
>
> On Thursday, February 26, 2015 at 11:23:31 PM UTC+2, Aaron Meurer wrote:
>>
>> See http://docs.sympy.org/latest/tutorial/simplification.html#powers.
>> powsimp(expr, force=True) will do what you want.
>>
>> Aaron Meurer
>>
>> On Thu, Feb 26, 2015 at 12:18 PM, Paul Royik <[email protected]> wrote:
>> > I need something more general
>> >
>> > On Thursday, February 26, 2015 at 7:50:15 PM UTC+2, John Peterson wrote:
>> >>
>> >>
>> >>
>> >> On Thursday, February 26, 2015 at 8:32:11 AM UTC-7, Paul Royik wrote:
>> >>>
>> >>> What is the best way to convert sqrt(x)*sqrt(x-4) to sqrt(x^2-4x) or
>> >>> (x^2+5x+4)/sqrt(x)/sqrt(x-4) to (x^2+5x+4)/sqrt(x^2-4x)
>> >>>
>> >>> I tried replace, but it doesn't work in second case.
>> >>
>> >>
>> >> Be careful, they aren't equal for all values of x, but subs() will do
>> >> this
>> >> if you are willing to be explicit...
>> >>
>> >>> #!/usr/bin/env python
>> >>> from sympy import *
>> >>> print sympify('(x**2 + 5*x + 4) / sqrt(x) /
>> >>> sqrt(x-4)').subs(sympify('sqrt(x)*sqrt(x-4)'), sympify('sqrt(x**2 -
>> >>> 4*x)'))
>> >>
>> >>
>> >> Output:
>> >>
>> >>> (x**2 + 5*x + 4)/sqrt(x**2 - 4*x)
>> >>
>> >>
>> >
>> > --
>> > You received this message because you are subscribed to the Google
>> > Groups
>> > "sympy" group.
>> > To unsubscribe from this group and stop receiving emails from it, send
>> > an
>> > email to [email protected].
>> > To post to this group, send email to [email protected].
>> > Visit this group at http://groups.google.com/group/sympy.
>> > To view this discussion on the web visit
>> >
>> > https://groups.google.com/d/msgid/sympy/a20128fc-d1bd-479e-8845-a581cfc6b7d4%40googlegroups.com.
>> >
>> > For more options, visit https://groups.google.com/d/optout.
>
> --
> You received this message because you are subscribed to the Google Groups
> "sympy" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to [email protected].
> To post to this group, send email to [email protected].
> Visit this group at http://groups.google.com/group/sympy.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/sympy/dc099057-8529-4f12-ae42-ed7f9e89b98e%40googlegroups.com.
>
> For more options, visit https://groups.google.com/d/optout.
--
You received this message because you are subscribed to the Google Groups
"sympy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sympy.
To view this discussion on the web visit
https://groups.google.com/d/msgid/sympy/CADDwiVBFuyH-70xMQUH4mFRUaq-_aze1CmCsbZyPZVF6qHbGLA%40mail.gmail.com.
For more options, visit https://groups.google.com/d/optout.
