It doesn't work because you've hard-coded the symbol x into the
function, and then used a different one in the tests (Symbol("x",
real=True) != Symbol("x")). Generally functions like this take a
parameter for the variable, like Delta(expr, x, d=1).
Unrelated: why are you using integrate to compute this? That is very
inefficient, and won't always work. Just use subs.
Aaron Meurer
On Jul 7, 2012, at 11:08 PM, Saurabh Jha <saurabh.j...@gmail.com> wrote:
> This is the code along with documentation
>
> from sympy import diff, integrate, sympify, expand, Symbol
> x=Symbol('x')
> def Delta(expr, d = 1):
> """Takes as input function expression and returns the diffrence
> between final value(function's expression incremented to 1) and
> initial value (function's expression).
>
>>>> from sympy import Symbol
>>>> from sympy import sin, cos
>>>> from sympy.series.integrals import Delta
>>>> x = Symbol('x')
>>>> Delta(x**2 + 3*x -2)
> 2*x + 4
>>>> Delta(sin(x))
> - sin(x) + sin(x + 1)
>
> If you want an increment different than 1, you can give it the
> increment value as an argument to Delta
> as shown below
>>>> Delta(x**2 - 2*x + 3, 2)
> 4*x
>>>> Delta(x**3 + 3*x**2 + 4*x + 5, 3)
> 9*x**2 + 45*x + 66
> """
>
> expr=sympify(expr)
> a=diff(expr)
> b=integrate(a, (x, x, x+d))
> expand(b)
> return expand(b)
>
>
>
> and these are the tests
>
> from sympy import sin, cos
> from sympy import pi
> from sympy import Symbol
> from sympy.series.kauers import Delta
> x = Symbol('x', real=True)
> m = Symbol('m', real=True)
>
>
> def test_Delta():
> assert Delta(x**2 + 2*x + 1) == 2*x + 3
> assert Delta(x**3 + 2*x**2 + 3*x +5) == 3*x**2 + 7*x + 6
> assert Delta(x**2 - 2*x + 3) == 2*x - 1
> assert Delta(x**2 + 3*x -2) == 2*x + 4
> assert Delta(sin(x), pi/6) == -sin(x) + sin(x + pi/6)
> assert Delta(cos(x), pi/3)
> assert Delta(x**2 - 2*x + 3, 2) == 4*x
> assert Delta(x**2 - 2*x + 3, 3) == 6*x + 3
>
>
>
>
> On Jul 8, 7:59 am, Aaron Meurer <asmeu...@gmail.com> wrote:
>> It's hard to tell without seeing the code. What you wrote should work.
>>
>> Aaron Meurer
>>
>> On Jul 7, 2012, at 5:44 AM, Saurabh Jha <saurabh.j...@gmail.com> wrote:
>>
>>
>>
>>
>>
>>
>>
>>> Hi,
>>
>>> I implemented a Delta() function as a part of my project of
>>> implementation of Kauers' algorithm
>>
>>> It takes as input function expression and returns the difference
>>> between final value(function's expression incremented to 1) and
>>> initial value (function's expression)
>>> .
>>> I saved the changes and ran it from sympy at python IDLE as
>>> follows
>>
>>>>>> Delta(x**2 + 2*x + 1)
>>> 2*x + 3
>>
>>> But when I wrote the tests as
>>
>>> assert Delta(x**2 + 2*x + 1) == 2*x + 3
>>
>>> it printed assertion error
>>
>>> The tests diden't passed. I don't know what's the differenece between
>>> the two situations, please help me figure it out
>>
>>> -Saurabh Jha
>>
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