Hi Aaron,
Thanks for the reply. One of the main things I'm hoping to do is make
absolute values go away. I frequently in my code am getting things like (x
- y) / Abs(x - y). I know x - y is > 0, so this is just 1.
I should note that when I run your code, I get the following:
In [1]: x, y = symbols('x y')
In [2]: refine(sqrt((x - y)**2))
Out[2]:
__________
╱ 2
╲╱ (x - y)
In [3]: Q.positive(x - y)
Out[3]: Q.positive(x - y)
In [4]: refine(sqrt((x - y)**2))
Out[4]:
__________
╱ 2
╲╱ (x - y)
On Mon, Nov 10, 2014 at 7:13 PM, Aaron Meurer <[email protected]> wrote:
> Q is just a namespace for the assumptions, like Q.positive or Q.real.
>
> refine() simplifies things based on assumptions. This example returns x -
> y, because sqrt((x - y)**2) is equal to x - y if x - y is positive (but not
> in general).
>
> What kinds of simplifications are you expecting to get out of your
> constraints?
>
> Aaron Meurer
>
>
> On Mon, Nov 10, 2014 at 5:42 PM, Andrew Spielberg <[email protected]>
> wrote:
>
>> Hi Aaron,
>>
>> Thanks for the speedy reply. I'm not sure I fully understand what this
>> example does, or how. Could you perhaps elaborate? What is Q? What is
>> the difference between refine and simplify?
>>
>> I should note that the entirety of my constraints will be linear, so if
>> the current functionality can do that, that's enough.
>>
>> -Andy S.
>>
>> On Mon, Nov 10, 2014 at 5:06 PM, Aaron Meurer <[email protected]> wrote:
>>
>>> There is a framework to do this with refine, like refine(sqrt((x -
>>> y)**2), Q.positive(x - y)), but not much is implemented yet, so the
>>> simplifications possible are quite limited (in fact, there's not much more
>>> than the one that I just showed that is implemented).
>>>
>>> Aaron Meurer
>>>
>>> On Mon, Nov 10, 2014 at 3:58 PM, Andrew Spielberg <[email protected]
>>> > wrote:
>>>
>>>> Hi all,
>>>>
>>>> When creating variables, I know you can provide certain constraints on
>>>> the domain of that variable. For instance, one could say that a certain
>>>> variable, x, is positive, real, rational, etc. These constraints affect
>>>> the way the simplify function behaves.
>>>>
>>>> I am wondering, without creating auxiliary variables, can add other
>>>> constraints? For example, if I have a variable x that always must be
>>>> greater than another variable y, can I specify:
>>>>
>>>> x > y
>>>>
>>>> in some way, and have the simplifier intelligently know how to handle
>>>> it? I know I could change my representation to be a = (x - y) and do
>>>> everything in terms of my variable a, and set a positive, but this is less
>>>> than ideal and will not work in a lot of my cases.
>>>>
>>>> If there is no way to set these assumptions, is there some other
>>>> recommended way to do intelligent simplification in some way?
>>>>
>>>> -Andy S.
>>>>
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