Update: The following is now possible, and should work in Sage 4.6, thanks to Burcin:
sage: x*x
x^2
sage: x.mul(x, hold=True)
x*x
sage: sin(2*pi)
0
sage: sin(2*pi,hold=True)
sin(2*pi)
More documentation can be found in each symbolic function, and x.mul? and x.add?.
In theory we could create a global hold context - see http://trac.sagemath.org/sage_trac/ticket/10035. I don't think this will be done any time soon, though.
What's the status of this issue? I agree with twk, that this is a little gnarly to type. Without this nicely implemented, it's almost impossible to know if the simplification makes sense, or even what your input was interpreted as. It's certainly barrier to new students, and even more experienced folks.
I do like the way WolframAlpha handles this. In this example, it checks to see if this expression is true (unsimplified on one side, simplified on the other):
x*x*x == x**3
http://www.wolframalpha.com/input/?i=xxx+%3D%3D+x**3
I know it's not what you mean, but you can use strings:
sage: ex = "2*x+2*x"
sage: ex
'2*x+2*x'
sage: var('x')
sage: sage_eval(ex, locals = globals())
4*x
But for example you don't get the correct latex representation of ex when you do latex(ex), it's just typed as a string.
The above code would not be the place to start for actually implementing this feature. To actually do this, you'd have to work on Pynac which is a C++ library based on GiNaC. It may have some internal assumptions that things are already simplified to a certain extent.
No, there is no way to do this at present. A "hold" feature for symbolic expressions is something that has been requested a million times on sage-support. I know that Burcin has been thinking about implementing something like this. But it is current not possible.
Asked: 2010-08-18 20:45:10 +0100
Seen: 2,990 times
Last updated: Feb 10 '11
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Hi, any updates on this topic? I still think, that this is a big disadvantage in symbolic calculations in sage!
is the "hold=True" option in Sage 4.6 not sufficient?