[sympy] Should symbolic integration fail gracefully?
It seems as though the symbolic integration process fails when it can't
find a solution:
integrate(sin(x**n),x)
Traceback (most recent call last):
File "", line 1, in
File
"C:\SymPyWorkbook\lib\site-packages\sympy\integrals\integrals.py", line
1477, in integrate
return integral.doit(**doit_flags)
File
"C:\SymPyWorkbook\lib\site-packages\sympy\integrals\integrals.py", line
541, in doit
function, xab[0], **eval_kwargs)
File
"C:\SymPyWorkbook\lib\site-packages\sympy\integrals\integrals.py", line
1012, in _eval_integral
h = meijerint_indefinite(g, x)
File
"C:\SymPyWorkbook\lib\site-packages\sympy\integrals\meijerint.py", line
1621, in meijerint_indefinite
res = _meijerint_indefinite_1(f.subs(x, x + a), x)
File
"C:\SymPyWorkbook\lib\site-packages\sympy\integrals\meijerint.py", line
1684, in _meijerint_indefinite_1
if b < 0 or f.subs(x, 0).has(nan, zoo):
File "C:\SymPyWorkbook\lib\site-packages\sympy\core\relational.py",
line 304, in __nonzero__
raise TypeError("cannot determine truth value of Relational")
TypeError: cannot determine truth value of Relational
I suppose I expected it to return an unevaluated integral -
integral(sin(x**n),x)
David
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Re: [sympy] Should symbolic integration fail gracefully?
Hi David,
Can you open an issue on Github please. That's a bug that should be fixed.
Oscar
On Tue, 20 Aug 2019 at 21:08, David Bailey wrote:
>
> It seems as though the symbolic integration process fails when it can't find
> a solution:
>
> integrate(sin(x**n),x)
> Traceback (most recent call last):
> File "", line 1, in
> File "C:\SymPyWorkbook\lib\site-packages\sympy\integrals\integrals.py",
> line 1477, in integrate
> return integral.doit(**doit_flags)
> File "C:\SymPyWorkbook\lib\site-packages\sympy\integrals\integrals.py",
> line 541, in doit
> function, xab[0], **eval_kwargs)
> File "C:\SymPyWorkbook\lib\site-packages\sympy\integrals\integrals.py",
> line 1012, in _eval_integral
> h = meijerint_indefinite(g, x)
> File "C:\SymPyWorkbook\lib\site-packages\sympy\integrals\meijerint.py",
> line 1621, in meijerint_indefinite
> res = _meijerint_indefinite_1(f.subs(x, x + a), x)
> File "C:\SymPyWorkbook\lib\site-packages\sympy\integrals\meijerint.py",
> line 1684, in _meijerint_indefinite_1
> if b < 0 or f.subs(x, 0).has(nan, zoo):
> File "C:\SymPyWorkbook\lib\site-packages\sympy\core\relational.py", line
> 304, in __nonzero__
> raise TypeError("cannot determine truth value of Relational")
> TypeError: cannot determine truth value of Relational
>
> I suppose I expected it to return an unevaluated integral -
> integral(sin(x**n),x)
>
> David
>
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Re: [sympy] Should symbolic integration fail gracefully?
"TypeError: cannot determine truth value of Relational" generally
indicates a bug in SymPy. And yes, integrate() should always return
unevaluated when it can't compute the integral.
Aaron Meurer
On Tue, Aug 20, 2019 at 2:08 PM David Bailey wrote:
>
> It seems as though the symbolic integration process fails when it can't find
> a solution:
>
> integrate(sin(x**n),x)
> Traceback (most recent call last):
> File "", line 1, in
> File "C:\SymPyWorkbook\lib\site-packages\sympy\integrals\integrals.py",
> line 1477, in integrate
> return integral.doit(**doit_flags)
> File "C:\SymPyWorkbook\lib\site-packages\sympy\integrals\integrals.py",
> line 541, in doit
> function, xab[0], **eval_kwargs)
> File "C:\SymPyWorkbook\lib\site-packages\sympy\integrals\integrals.py",
> line 1012, in _eval_integral
> h = meijerint_indefinite(g, x)
> File "C:\SymPyWorkbook\lib\site-packages\sympy\integrals\meijerint.py",
> line 1621, in meijerint_indefinite
> res = _meijerint_indefinite_1(f.subs(x, x + a), x)
> File "C:\SymPyWorkbook\lib\site-packages\sympy\integrals\meijerint.py",
> line 1684, in _meijerint_indefinite_1
> if b < 0 or f.subs(x, 0).has(nan, zoo):
> File "C:\SymPyWorkbook\lib\site-packages\sympy\core\relational.py", line
> 304, in __nonzero__
> raise TypeError("cannot determine truth value of Relational")
> TypeError: cannot determine truth value of Relational
>
> I suppose I expected it to return an unevaluated integral -
> integral(sin(x**n),x)
>
> David
>
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Re: [sympy] Can't get sympy.functions.atan2 to work with _eval_evalf
On Tuesday, August 20, 2019 at 5:43:40 PM UTC+3, Oscar wrote: > > Can you open an issue on Github for this? > > Sure: https://github.com/sympy/sympy/issues/17461 -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sympy+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/73823501-26d0-403b-b28b-20b98fb82fda%40googlegroups.com.
Re: [sympy] Can't get sympy.functions.atan2 to work with _eval_evalf
There's a "return" missing:
$ git diff
diff --git a/sympy/functions/elementary/trigonometric.py
b/sympy/functions/elementary/trigonometric.py
index 635e7f2..b7a0ad1 100644
--- a/sympy/functions/elementary/trigonometric.py
+++ b/sympy/functions/elementary/trigonometric.py
@@ -3070,4 +3070,4 @@ def fdiff(self, argindex):
def _eval_evalf(self, prec):
y, x = self.args
if x.is_extended_real and y.is_extended_real:
-super(atan2, self)._eval_evalf(prec)
+return super(atan2, self)._eval_evalf(prec)
Also it checks if the args are real so it looks like you might need to
declare your variables a and y with real=True. If you do that then the
result is caculated as: 0.785398163397448
Can you open an issue on Github for this?
On Tue, 20 Aug 2019 at 15:34, Ville Bergholm wrote:
>
> I've been trying to use sympy.Symbol to implement a system where the
> numerical value of a symbolic quantity is only fixed when it is evaluated
> using evalf().
> To accomplish this I've redefined _eval_evalf() to return the aforementioned
> value (a fixed 5.0 in the toy example below).
>
> This works fine with basic algebraic operations and most SymPy functions.
> However, for some reason atan2 seems to behave differently and _eval_evalf is
> never called.
> Is this a bug, or have I misunderstood the purpose of _eval_evalf?
>
>
> import sympy
> import sympy.functions as syf
>
> class A(sympy.Symbol):
> def _eval_evalf(self, prec):
> print('*')
> return sympy.Float(5.0)
>
> x = A('X')
> y = A('Y')
> print('polynomial:')
> print((2*x-4+y).evalf()) # works fine
> print('atan:')
> print(syf.atan(y / x).evalf()) # works fine
> print('beta:')
> print(syf.beta(y, x).evalf()) # works fine
> print('atan2:')
> print(syf.atan2(y, x).evalf()) # prints "atan2(Y, X)", does not call
> A._eval_evalf
>
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[sympy] Can't get sympy.functions.atan2 to work with _eval_evalf
I've been trying to use sympy.Symbol to implement a system where the
numerical value of a symbolic quantity is only fixed when it is evaluated
using evalf().
To accomplish this I've redefined _eval_evalf() to return the
aforementioned value (a fixed 5.0 in the toy example below).
This works fine with basic algebraic operations and most SymPy functions.
However, for some reason atan2 seems to behave differently and _eval_evalf
is never called.
Is this a bug, or have I misunderstood the purpose of _eval_evalf?
import sympy
import sympy.functions as syf
class A(sympy.Symbol):
def _eval_evalf(self, prec):
print('*')
return sympy.Float(5.0)
x = A('X')
y = A('Y')
print('polynomial:')
print((2*x-4+y).evalf()) # works fine
print('atan:')
print(syf.atan(y / x).evalf()) # works fine
print('beta:')
print(syf.beta(y, x).evalf()) # works fine
print('atan2:')
print(syf.atan2(y, x).evalf()) # prints "atan2(Y, X)", does not call
A._eval_evalf
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[sympy] Re: Can't get sympy.functions.atan2 to work with _eval_evalf
It seems that evalf of atan2 currently expects that its arguments are real.
For symbols like x and y, this
means that they have to be initialized with `real=True`. It does not
suffice that evalf would return a real
value as assumption code does not try to run evalf.
Kalevi Suominen
On Tuesday, August 20, 2019 at 5:34:21 PM UTC+3, Ville Bergholm wrote:
>
> I've been trying to use sympy.Symbol to implement a system where the
> numerical value of a symbolic quantity is only fixed when it is evaluated
> using evalf().
> To accomplish this I've redefined _eval_evalf() to return the
> aforementioned value (a fixed 5.0 in the toy example below).
>
> This works fine with basic algebraic operations and most SymPy functions.
> However, for some reason atan2 seems to behave differently and _eval_evalf
> is never called.
> Is this a bug, or have I misunderstood the purpose of _eval_evalf?
>
>
> import sympy
> import sympy.functions as syf
>
> class A(sympy.Symbol):
> def _eval_evalf(self, prec):
> print('*')
> return sympy.Float(5.0)
>
> x = A('X')
> y = A('Y')
> print('polynomial:')
> print((2*x-4+y).evalf()) # works fine
> print('atan:')
> print(syf.atan(y / x).evalf()) # works fine
> print('beta:')
> print(syf.beta(y, x).evalf()) # works fine
> print('atan2:')
> print(syf.atan2(y, x).evalf()) # prints "atan2(Y, X)", does not call
> A._eval_evalf
>
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