Status: Valid
Owner: ----
Labels: Type-Defect Priority-Medium
New issue 3987 by [email protected]: wrong tests in test_deltaproduct
http://code.google.com/p/sympy/issues/detail?id=3987
In ``test_deltaproduct`` there are two tests which seem wrong to me;
the second of them takes a long time; that's the reason I looked at it.
The first one is
```
assert dp((x + y)*(y + KD(i, j)), (j, 1, k)) == ((x + y)*y)**k + \
((x + y)*y)**(i - 1)*(x + y)*((x + y)*y)**(k - i)
```
For ``k=1`` the LHS is ``(x + y)*(y + KD(i, 1))``, the RHS is
``(x+y)*(y+1)``
so they differ for ``i != 1``.
The second one gives a similar error
```
assert dp((x + y)*(y + KD(i, j)), (j, k, 3)) == ((x + y)*y)**(-k + 4) + \
((x + y)*y)**(i - k)*(x + y)*((x + y)*y)**(3 - i)
```
For ``k=3`` the LHS is ``(x+y)*(y+KD(i,3))``, the RHS is ``(x+y)*(y+1)``
There are other tests which seem wrong to me; for instance
``assert dp(KD(i, j), (j, k, 3)) == KD(i, 3)*KD(k, 3) + KD(k, 4)``
For ``k = 5`` the LHS is 1, the RHS is 0.
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