Hi friends, please allow me to introduce myself. My name is Mike Roberts. I
am a computer science PhD student at Stanford. I've been using sympy
recently to help me solve some fun optimization problems.
I have encountered some unexpected behavior in the sympy.utilities.autowrap
module.
I believe I am running into an undocumented hard-coded limit on the number
of symbols I can pass into sympy.utilities.autowrap.ufuncify(...). Here is
the code snippet that demonstrates the unexpected behavior I'm seeing.
from pylab import *
import sympy
import sympy.utilities.autowrap
zero_expr = sympy.sympify("0")
num_syms = 31
syms = [ sympy.Symbol("x_%02d"%i) for i in range(num_syms) ]
vals = zeros(len(syms))
zero_expr_ufuncify =
sympy.utilities.autowrap.ufuncify(args=syms,expr=zero_expr,backend="numpy",verbose=True)
# works
print zero_expr_ufuncify(*vals)
print
num_syms = 31
syms = [ sympy.Symbol("x_%099d"%i) for i in range(num_syms) ]
vals = zeros(len(syms))
zero_expr_ufuncify =
sympy.utilities.autowrap.ufuncify(args=syms,expr=zero_expr,backend="numpy",verbose=True)
# also works
print zero_expr_ufuncify(*vals)
print
num_syms = 32
syms = [ sympy.Symbol("x_%02d"%i) for i in range(num_syms) ]
vals = zeros(len(syms))
zero_expr_ufuncify =
sympy.utilities.autowrap.ufuncify(args=syms,expr=zero_expr,backend="numpy",verbose=True)
# doesn't work
print "about to evaluate ufunc with 32 args..."
print zero_expr_ufuncify(*vals)
print
The first two calls to zero_expr_ufuncify(*vals) behave as expected,
returning 0.0. But the last call to zero_expr_ufuncify(*vals) causes a
segmentation fault. The exact error I'm getting is as follows.
Segmentation fault: 11
The only difference between these calls is that
sympy.utilities.autowrap.ufuncify(...) was called with symbol lists of
different lengths. For both behaves-as-expected calls, the corresponding
symbol list is of length 31. For the does-not-behave-as-expected call, the
corresponding symbol list is of length 32.
Note that the second call has a corresponding symbol list of length 31, but
the symbols have very long names. Since this call behaves as expected, I
believe this is not a problem of the generated C code having too many ASCII
characters on a single line.
Note that I also found a post describing a similar issue on the Google
Group. However, the code example from the Google Group is targeting a
Fortran backend. Therefore, I believe the issue on the Google Group is
different to the one I'm reporting here.
https://groups.google.com/forum/#!searchin/sympy/ufuncify/sympy/kgzcR8Qu7s4/RAGTw7A0I3oJ
I'm running sympy 0.7.6-1, which I installed via the Canopy Package Manager
on OSX Yosemite 10.10.3, 64 bit.
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