If you're willing to keep your index knowledge around separately you can
build a matrix expression and then subs in immutableMatrices
X, Y = MatrixSymbol('X', 2, 2), MatrixSymbol('Y', 2, 2)
idx = (0, 1)
expr = (X+Y)*Y
nx, ny = ImmutableMatrix(...), ImmutableMatrix(...)
expr.subs({X: nx, Y: ny})[idx[0], idx[1]]
On Thu, Nov 1, 2012 at 1:42 PM, Matthew Rocklin <[email protected]> wrote:
> Short answer, you can't yet. Current issues are as follows
>
> MatrixExprs doesn't yet support fancy indexing so you'll have to be
> explicit and use p[i, j] and not p[i] --- this could be fixed by improving
> the `__getitem__` method in MatrixExpr
>
> p[i, j] yields a Symbol with the name "%s_ij"%p.name . This object has no
> connection back to the original p. --- this could be fixed by creating some
> sort of Element(Symbol) class.
>
>
> On Thu, Nov 1, 2012 at 1:36 PM, Stefan Krastanov <
> [email protected]> wrote:
>
>> This is unrelated to the previous question about matrix expressions.
>>
>> How can I do the following
>>
>>
>> >>> p = MatrixSymbol('p', 2, 1)
>> >>> p[0].subs(p, Matrix([5, 6]))
>> 5
>> >>> p[x].subs(p, Matrix([5, 6])).subs(x, 0)
>> 5
>>
>> The first one is more important for me than the second one.
>>
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