C code from IndexedBase

[Nico Schlömer]

From an object like `sin(u[k]) + u0[k]` I would like to get the corresponding C code as a string. Since `k` is a variable, I cannot use `MatrixSymbol`, but there's always `IndexedBase` of course. With

```

u = IndexedBase('u')

u0 = IndexedBase('u0')

k = Symbol('k')

y = sin(u[k]) + u0[k]

```

things are looking good, but then

```

from sympy.utilities.codegen import codegen

[(c_name, c_code), (h_name, c_header)] = codegen(("f", y), "C")

```

tells you

```

sympy.tensor.indexed.IndexException: 

Range is not defined for all indices in: u[k]

```

I could perhaps go through all `IndexedBase` instances in `y` and `.subs`titute them with a variable with the string `u[k]`, but that feels hackish.

Any hints?

[Nico Schlömer]

It seems that, unfortunately, the information of whether or not a variable is an IndexedBase object is discarded when using it in an expression. Check

```

from sympy import *

u = IndexedBase('u')

k = Symbol('k')

y = u[k]

print(isinstance(u, IndexedBase))

for s in y.free_symbols:

    print(s, isinstance(s, IndexedBase))

```

Hm...

[Nico Schlömer]

Once again, atoms to the rescue.

```

y.atoms(IndexedBase)

```

will give you all IndexedBase object from an expression.

[Francesco Bonazzi]

Have you tried to use Idx instead of Symbol for the index?

k = Idx("k", 4)

4 is the range.

In this case, k ranges from 0 to 4-1 = 3.

[Aaron Meurer]

I would consider this to be a bug. You should open an issue for it.

If you use Idx as Francesco suggests, there is a different error

ValueError: lhs indices must match non-dummy rhs indices in sin(u[k]) + u0[k]

which also looks like a bug.

Aaron Meurer

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