#7742: add a compose function to sage
------------------------------------------------+---------------------------
Reporter: was | Owner: AlexGhitza
Type: defect | Status: needs_work
Priority: major | Milestone: sage-4.6.1
Component: basic arithmetic | Keywords:
Author: Christopher Olah, Felix Lawrence | Upstream: N/A
Reviewer: Paul Zimmermann | Merged:
Work_issues: |
------------------------------------------------+---------------------------
Changes (by zimmerma):
* status: needs_review => needs_work
Comment:
I am not very happy with the fact that when f is an expression, the code
assumes it has exactly
one symbolic variable:
{{{
sage: f = 2
sage: self_compose(f,0)
<function <lambda> at 0x41031b8>
sage: self_compose(f,1)
2
sage: self_compose(f,2)
<function <lambda> at 0x7fa8ac2b0d70>
}}}
or
{{{
sage: f = x+y
sage: self_compose(f,0)
x
sage: self_compose(f,1)
x + y
sage: self_compose(f,2)
x + 2*y
}}}
Consider also:
{{{
sage: f = pi+1
sage: self_compose(f,0)
---------------------------------------------------------------------------
IndexError Traceback (most recent call
last)
/tmp/cado-nfs-1.0-rc1/<ipython console> in <module>()
/usr/local/sage-4.6/sage/local/lib/python2.6/site-
packages/sage/misc/misc.pyc in self_compose(f, n)
911 if n == 0:
912 if type(f) == sage.symbolic.expression.Expression:
--> 913 return f.parent()(f.variables()[0])
914 else:
915 return lambda x: x
IndexError: tuple index out of range
}}}
I would prefer that symbolic expressions such as {{{f=x+1}}} are not
allowed,
and we should write instead {{{f(x)=x+1}}} or {{{f = lambda x : x+1}}}.
Paul
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7742#comment:25>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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