#12302: Partial evaluation bug for callable vector functions
-------------------------+--------------------------------------------------
Reporter: gbe | Owner: gbe
Type: defect | Status: new
Priority: major | Milestone: sage-5.0
Component: symbolics | Keywords: sd35.5
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
-------------------------+--------------------------------------------------
Description changed by gbe:
Old description:
> For callable (scalar) functions, taking sections (partial evaluation) of
> functions works perfectly fine; that is to say the following code works
> perfectly as expected:
> {{{
> sage: f(x,y,z) = x*y*z; f
> (x, y, z) |--> x*y*z
> sage: g(x, z) = f(y=1); g
> (x, z) |--> x*z
> }}}
>
> Move up to callable vector functions and taking sections breaks however:
> {{{
> sage: v(x, y) = [x+y, x-y]; v
> (x, y) |--> (x + y, x - y)
> sage: v(x,0)
> (x, x)
> sage: w(x) = v(y=0)
> TypeError
> }}}
>
> '''This is because ''all'' evaluation, even if partial, of a callable
> vector function returns a Vector_symbolic_dense.'''
>
> The fix, of course, is to make the code intelligent enough to know that
> an evaluation is only partial -- one hopes that ``type(vx)`` would return
> 'sage.modules.vector_callable_symbolic_dense.Vector_callable_symbolic_dense'>
> rather than 'sage.modules.vector_symbolic_dense.Vector_symbolic_dense'>
> {{{
> sage: v(x, y) = [x+y, x-y]
> sage: type(v)
> <class
> 'sage.modules.vector_callable_symbolic_dense.Vector_callable_symbolic_dense'>
> sage: vx = v(y=0); vx
> (x,x)
> sage: type(vx)
> <class 'sage.modules.vector_symbolic_dense.Vector_symbolic_dense'>
> }}}
>
> '''Work-around'''
>
> This isn't ''so'' bad since we can still do:
> {{{
> sage: v(x, y) = [x+y, x-y]
> sage: vx = v(y=0)
> }}}
>
> Now, if every entry still has a variable everything, including positional
> rather than named arguments work.
> {{{
> sage: v(x, y) = [x+y, x-y]
> sage: vx = v(y=0)
> sage: vx(x=1)
> (1, 1)
> sage: vx(1) #deprecated, but works fine
> }}}
>
> However, things break if taking a section kills off all variables in any
> component we try to use positional arguments:
> {{{
> sage: v(x, y) = [x+y, x-y]
> sage: vy = v(y=x)
> sage: vy
> (2*x, 0)
> sage: vx
> (x, x)
> sage: vy(x=1) #named arguments still work
> (2, 0)
> sage: vy(1) #positional arguments don't
> ValueError
> }}}
New description:
For callable (scalar) functions, taking sections (partial evaluation) of
functions works perfectly fine; that is to say the following code works
perfectly as expected:
{{{
sage: f(x,y,z) = x*y*z; f
(x, y, z) |--> x*y*z
sage: g(x, z) = f(y=1); g
(x, z) |--> x*z
}}}
Move up to callable vector functions and taking sections breaks however:
{{{
sage: v(x, y) = [x+y, x-y]; v
(x, y) |--> (x + y, x - y)
sage: v(x,0)
(x, x)
sage: w(x) = v(y=0)
TypeError
}}}
'''This is because ''all'' evaluation, even if partial, of a callable
vector function returns a Vector_symbolic_dense.'''
The fix, of course, is to make the code intelligent enough to know that an
evaluation is only partial -- one hopes that ``type(vx)`` would return
'sage.modules.vector_callable_symbolic_dense.Vector_callable_symbolic_dense'>
rather than 'sage.modules.vector_symbolic_dense.Vector_symbolic_dense'>
{{{
sage: v(x, y) = [x+y, x-y]
sage: type(v)
<class
'sage.modules.vector_callable_symbolic_dense.Vector_callable_symbolic_dense'>
sage: vx = v(y=0); vx
(x,x)
sage: type(vx)
<class 'sage.modules.vector_symbolic_dense.Vector_symbolic_dense'>
}}}
'''Work-around'''
This isn't ''so'' bad since we can still do:
{{{
sage: v(x, y) = [x+y, x-y]
sage: vx = v(y=0)
}}}
Now, if every entry still has a variable everything, including positional
rather than named arguments, works.
{{{
sage: v(x, y) = [x+y, x-y]
sage: vx = v(y=0)
sage: vx(x=1)
(1, 1)
sage: vx(1) #deprecated, but works fine
}}}
However, things break if taking a section kills off all variables in any
component we try to use positional arguments:
{{{
sage: v(x, y) = [x+y, x-y]
sage: vy = v(y=x)
sage: vy
(2*x, 0)
sage: vx
(x, x)
sage: vy(x=1) #named arguments still work
(2, 0)
sage: vy(1) #positional arguments don't
ValueError
}}}
--
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12302#comment:1>
Sage <http://www.sagemath.org>
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and MATLAB
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