ccode user_functions arg does not work for sqrt, fabs, pow?

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John Peterson

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Feb 26, 2015, 11:56:01 AM2/26/15
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Hi,

It's entirely possible I'm using ccode wrong, but I can't seem to get it to recognize my custom replacements for sqrt, fabs, or pow.  Here's a simple test case:

#!/usr/bin/env python
from sympy import *
 
print ccode(sympify('sqrt(x)'), user_functions={"sqrt": "std::sqrt"})
print ccode(sympify('Abs(x)'), user_functions={"fabs": "std::abs"})
print ccode(sympify('x**2'), user_functions={"pow": "std::pow"})

On my system, this prints:

sqrt(x)
fabs(x)
pow(x, 2)


I can of course work around this pretty easily with text replacement, so it's not a big deal...

Jason Moore

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Feb 26, 2015, 12:53:30 PM2/26/15
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John,

The key's to the user_functions dictionary should be strings that map to SymPy functions in the expressions:

In [18]: print sympy.ccode(sympy.sin(sympy.symbols('x')), user_functions={"sin": "std::sin"})
std::sin(x)

In [19]: print sympy.ccode(sympy.Abs(sympy.symbols('x')), user_functions={"Abs": "std::abs"})
std::abs(x)



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Jason Moore

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Feb 26, 2015, 12:54:27 PM2/26/15
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Also this one isn't obvious:

In [21]: print sympy.ccode(sympy.symbols('x')**2, user_functions={"Pow": "std::pow"})
std::pow(x, 2)

John Peterson

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Feb 26, 2015, 1:04:49 PM2/26/15
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On Thursday, February 26, 2015 at 10:54:27 AM UTC-7, Jason Moore wrote:
Also this one isn't obvious:

In [21]: print sympy.ccode(sympy.symbols('x')**2, user_functions={"Pow": "std::pow"})
std::pow(x, 2)

Interestingly, this line of code still prints pow(x,2) for me.  May be a different in Sympy version?  I am using 0.7.5.

Jason Moore

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Feb 26, 2015, 1:15:43 PM2/26/15
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I'm on 0.7.6, so maybe a bug was fixed.


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Jason Moore

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Feb 26, 2015, 1:17:14 PM2/26/15
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Another way to handle this is to sublcass the CCodePrinter and then define methods for the specific function names. You will have more control over the details if you do it that way.

Jason Moore

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Feb 26, 2015, 6:07:11 PM2/26/15
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I tried to clarify the docstring a bit here: https://github.com/sympy/sympy/pull/9062

Let me know if that is more helpful.

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