Divergence wrong in cylindrical coordinates?

[Alexander Lindsay]

Execution of the below code:

From sympy.vector import divergence, gradient, Vector, CoordSys3D

R = CoordSys3D('R', transformation='cylindrical')
divergence(R.i)

generates a zero result. I believe the result should be 1/r, right?

[Alexander Lindsay]

This patch fixes the bad behavior:

diff --git a/sympy/vector/operators.py b/sympy/vector/operators.py
index 2f303ee690..994894f379 100644
--- a/sympy/vector/operators.py
+++ b/sympy/vector/operators.py
@@ -362,6 +362,4 @@ def _diff_conditional(expr, base_scalar, coeff_1, coeff_2):
     """
     from sympy.vector.functions import express
     new_expr = express(expr, base_scalar.system, variables=True)
-    if base_scalar in new_expr.atoms(BaseScalar):
-        return Derivative(coeff_1 * coeff_2 * new_expr, base_scalar)
-    return S.Zero
+    return Derivative(coeff_1 * coeff_2 * new_expr, base_scalar)

Should I submit a PR?

[Alan Bromborsky]

If you are dealing with gradient you might find this link of interest -

https://galgebra.readthedocs.io/en/latest/module-components.html#differential-operators

the galgebra package is built on top of sympy.

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[Faisal Riyaz]

Hello,

This looks like a bug. Please do submit a PR.

Thanks

Faisal Riyaz

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[Alexander Lindsay]

PR here: https://github.com/sympy/sympy/pull/20047

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