Re: [sympy] what does Equal and == do in sympy
Hello,
Thanks for the help previously. I've run into a different issue with
regards to Eq.
Sympify will automatically convert Eq into ==
sympy.sympify('Eq(a, b)')
a == b
which if you sympify again will have the behavior you described originally.
sympy.sympify(str(sympy.sympify('Eq(a, b)')))
False
Do you know of any way to stop the converion of Eq to ==?
Thanks,
Rob
On Friday, April 27, 2012 at 5:29:53 PM UTC-5, Aaron Meurer wrote:
Equal is not anything. You've just created an undefined function
called Equal (Function('Equal')) with that sympify command.
What you are probably looking for is Eq() (or Equality()). This
creates a symbolic equality. You can manipulate different sides of
the equation using Eq.lhs and Eq.rhs, like
In [496]: Eq(x, y)
Out[496]: x = y
In [497]: Eq(x, y).lhs
Out[497]: x
In [498]: Eq(x, y).rhs
Out[498]: y
Eq() will reduce to True when or False when it can see that the
expressions are always equal or unequal:
In [504]: Eq(x, y).subs({x: 1, y: 1})
Out[504]: True
In [505]: Eq(x, y).subs({x: 1, y: 2})
Out[505]: False
== is a lot different. This is used to exactly compare expressions.
a == b will be a boolean, True if a and be are exactly equal and False
otherwise. I say exactly equal because == does structural
comparison, not mathematical comparison. So we have
In [499]: x*(y + z) == x*y + x*z
Out[499]: False
In [500]: x*(y + z) == x*(y + z)
Out[500]: True
If you want to do a mathematical comparison, the best way is to
subtract one expression from the other and pass it to simplify(), and
see if it goes to 0. For example:
In [501]: a = x*(y + z)
In [502]: b = x*y + x*z
In [503]: simplify(a - b)
Out[503]: 0
See http://docs.sympy.org/dev/gotchas.html#equals-signs for more
discussion on this.
Aaron Meurer
On Fri, Apr 27, 2012 at 4:16 PM, Robert phu...@gmail.com javascript:
wrote:
Hello,
I have a question about == and Equal in sympy.
Their behavior is strange to me.
In [108]: expr = sympy.simplify('Equal(A,B)')
In [111]: expr.subs(dict(A=1, B=1))
Equal(1, 1)
In [112]: expr = sympy.simplify('A==B')
In [113]: expr
False
In [115]: A = sympy.Symbol('A')
In [116]: B = sympy.Symbol('B')
In [117]: A==B
False
In [118]: sympy.__version__
'0.7.1'
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Re: [sympy] what does Equal and == do in sympy
I was able to write a LambdaPrinter that does what I want for the time
being:
class NonRelationalOpPrinter(lambdarepr.LambdaPrinter):
'''
from structures import symbolic
for op in ['Eq', 'Ne', 'Gt', 'Lt', 'Ge', 'Le']:
...
sympy.sympify((symbolic.NonRelationalOpPrinter().doprint(sympy.sympify('%s(%s(a,
b), c)' % (op, op)
(a == b) == c
(a != b) != c
(a b) c
(a b) c
(a = b) = c
(a = b) = c
'''
def _printRelation(self, expr, name):
return '%s(%s)' % (name, , .join(map(self._print, expr.args)))
def _print_Equality(self, expr):
return self._printRelation(expr, 'Equality')
def _print_Unequality(self, expr):
return self._printRelation(expr, 'Unequality')
def _print_GreaterThan(self, expr):
return self._printRelation(expr, 'GreaterThan')
def _print_LessThan(self, expr):
return self._printRelation(expr, 'LessThan')
def _print_StrictGreaterThan(self, expr):
return self._printRelation(expr, 'StrictGreaterThan')
def _print_StrictLessThan(self, expr):
return self._printRelation(expr, 'StrictLessThan')
On Friday, May 29, 2015 at 4:31:59 AM UTC-5, Robert wrote:
Hello,
Thanks for the help previously. I've run into a different issue with
regards to Eq.
Sympify will automatically convert Eq into ==
sympy.sympify('Eq(a, b)')
a == b
which if you sympify again will have the behavior you described originally.
sympy.sympify(str(sympy.sympify('Eq(a, b)')))
False
Do you know of any way to stop the converion of Eq to ==?
Thanks,
Rob
On Friday, April 27, 2012 at 5:29:53 PM UTC-5, Aaron Meurer wrote:
Equal is not anything. You've just created an undefined function
called Equal (Function('Equal')) with that sympify command.
What you are probably looking for is Eq() (or Equality()). This
creates a symbolic equality. You can manipulate different sides of
the equation using Eq.lhs and Eq.rhs, like
In [496]: Eq(x, y)
Out[496]: x = y
In [497]: Eq(x, y).lhs
Out[497]: x
In [498]: Eq(x, y).rhs
Out[498]: y
Eq() will reduce to True when or False when it can see that the
expressions are always equal or unequal:
In [504]: Eq(x, y).subs({x: 1, y: 1})
Out[504]: True
In [505]: Eq(x, y).subs({x: 1, y: 2})
Out[505]: False
== is a lot different. This is used to exactly compare expressions.
a == b will be a boolean, True if a and be are exactly equal and False
otherwise. I say exactly equal because == does structural
comparison, not mathematical comparison. So we have
In [499]: x*(y + z) == x*y + x*z
Out[499]: False
In [500]: x*(y + z) == x*(y + z)
Out[500]: True
If you want to do a mathematical comparison, the best way is to
subtract one expression from the other and pass it to simplify(), and
see if it goes to 0. For example:
In [501]: a = x*(y + z)
In [502]: b = x*y + x*z
In [503]: simplify(a - b)
Out[503]: 0
See http://docs.sympy.org/dev/gotchas.html#equals-signs for more
discussion on this.
Aaron Meurer
On Fri, Apr 27, 2012 at 4:16 PM, Robert phu...@gmail.com wrote:
Hello,
I have a question about == and Equal in sympy.
Their behavior is strange to me.
In [108]: expr = sympy.simplify('Equal(A,B)')
In [111]: expr.subs(dict(A=1, B=1))
Equal(1, 1)
In [112]: expr = sympy.simplify('A==B')
In [113]: expr
False
In [115]: A = sympy.Symbol('A')
In [116]: B = sympy.Symbol('B')
In [117]: A==B
False
In [118]: sympy.__version__
'0.7.1'
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[sympy] diff(x^x,x)
Hi, the online shell at http://live.sympy.org/ tells me diff(x^x,x) = 0 Why is that? Tom -- 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 post to this group, send email to sympy@googlegroups.com. Visit this group at http://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/5f6df3dd-904b-4d1a-afcc-9ce8ff0d7a50%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [sympy] diff(x^x,x)
On 29 May 2015 22:06, Thomas Leitz unruhsc...@gmail.com wrote: Hi, the online shell at http://live.sympy.org/ tells me diff(x^x,x) = 0 Why is that? ^ doesn't do what you're expecting in Python. Use ** for exponentiation. -- Oscar -- 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 post to this group, send email to sympy@googlegroups.com. Visit this group at http://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CAHVvXxSNEU1dGr9zKOXRq1uFQYYEz10qHNku0JmzGmCqBhAq2w%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
