Comparison failure

[Alexander Lindsay]

Hi all,

I am working on a pull request. When writing tests for the PR, I keep encountering false comparisons when the expressions I'm comparing appear to be the exact same. Example shown below:

In[80]: %paste
    result = manualintegrate(x**(3/2) * log(x), x)
    desired_result = 0.4*x**2.5*log(x) - 0.16*x**2.5
    print(result)
    print(desired_result)
    print(result == desired_result)
    assert result == desired_result
## -- End pasted text --
0.4*x**2.5*log(x) - 0.16*x**2.5
0.4*x**2.5*log(x) - 0.16*x**2.5
False
Traceback (most recent call last):
  File "/home/lindsayad/miniconda2/envs/python3SympyDev/lib/python3.5/site-packages/IPython/core/interactiveshell.py", line 2885, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-80-5bc67a132f24>", line 6, in <module>
    assert result == desired_result
AssertionError

Any suggestions on how to make these comparisons work?

[Aaron Meurer]

My guess is that it's an issue with floating point accuracy. Unless
you are testing floating point numbers directly, I would suggest
making all values in the expressions rational. To accurately test
floating point numbers, you generally have to check that the
difference is below some small epsilon (like 1e-15), which can be
annoying if they appear throughout an expression.

Aaron Meurer

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