#20438: Wrapper_cdf.call_c() drops imaginary part
-------------------------+-------------------------------------------------
Reporter: cswiercz | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-7.2
Component: cython | Keywords: fast_callable, interpreters,
Merged in: | wrapper_cdf
Reviewers: | Authors: cswiercz
Work issues: | Report Upstream: N/A
Commit: | Branch:
Stopgaps: | Dependencies:
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A `Wrapper_cdf` object is created by `fast_callable(f, vars=[],
domain=None)` when the domain is set to `CDF`. The standard method of
evaluating the function represented by the resulting object by simple
calling it behaves normally.
However, the Cython-accesible method `Wrapper_cdf.call_c(double_complex*
out, double_complex* in)` drops the imaginary component of the input and
output. A demonstration of this behavior is given in the following SMC
notebook:
https://cloud.sagemath.com/projects/846aa4b7-ec55-4613-98ed-
7111e2b0644d/files/Wrapper_cdf%20Test.html
The source code for `Wrapper_cdf` is generated by
`sage/src/sage_setup/autogen/interpreters.py`. Within, there are some
peculiar comments when it comes to defining the custom data type
`double_complex`. The following is from
[https://github.com/sagemath/sage/blob/master/src/sage_setup/autogen/interpreters.py#L2533
Line 2533] where the Cython header for `Wrapper_cdf` is defined.
{{{
# We need the type double_complex to work around
# http://trac.cython.org/ticket/869
# so this is a bit hackish.
cdef extern from "complex.h":
ctypedef double double_complex "double complex"
}}}
But this seems to define `double_complex` as a `double`, which explains
why the imaginary part is dropped. Since complex externs are not allowed
in Cython(?) I tried changing this line to
{{{
ctypedef double complex double_complex "double complex"
}}}
but the following compilation error is raised
{{{
[1/3] Cythonizing sage/ext/interpreters/wrapper_cdf.pyx
Error compiling Cython file:
------------------------------------------------------------
...
cdef extern from "interp_cdf.h":
double_complex interp_cdf(double_complex* args,
double_complex* constants,
PyObject** py_constants,
double_complex* stack,
int* code) except? -1094648119105371
^
------------------------------------------------------------
sage/ext/interpreters/wrapper_cdf.pyx:64:28: Not allowed in a constant
expression
}}}
This part of the wrapper code is generated by
[https://github.com/sagemath/sage/blob/master/src/sage_setup/autogen/interpreters.py#L3290
interpreters.py:3290]. Commenting out this `except?` part resolves the
compile issue as well as the missing imaginary part problems. Attached is
a patch which makes the appropriate `double_complex` fixes as well as,
probably erroneously, comments out the except so that the code compiles.
(''Motivation: I would like to directly call the underlying C function of
a `Wrapper_cdf` for performance purposes.'')
--
Ticket URL: <http://trac.sagemath.org/ticket/20438>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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