fix: Divergence free /= incompressibility (#21)

Divergence free is not the same incompressibility.

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non divergent => incompressible but incompressible => non divergent does
not hold

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Signed-off-by: Andrin Rehmann [email protected]

Author: andrinr

examples/cfd/demo.ipynb

@@ -416,7 +416,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "We define the loss function, which additionally ensures physical realism of the initial condition by penalizing the flow's divergence (incompressibility)."
+    "We define the loss function, which additionally ensures physical realism of the initial condition by penalizing the flow's divergence."
    ]
   },
   {