#11842: substitute_function doesn't work as expected in many cases
-----------------------------+----------------------------------------------
Reporter: mjo | Owner: burcin
Type: defect | Status: closed
Priority: major | Milestone: sage-duplicate/invalid/wontfix
Component: symbolics | Resolution: duplicate
Keywords: | Work issues:
Report Upstream: N/A | Reviewers: Burcin Erocal
Authors: | Merged in:
Dependencies: | Stopgaps:
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Description changed by mjo:
Old description:
> I'm working on polynomial interpolation at the moment, and these are
> starting to hurt. Most of them have workarounds, but there don't seem to
> be any for the expressions involving derivatives.
>
> I've also tried with subs() and the like, but one step at a time.
>
> {{{
> from sage.all import *
>
> # 1. Fails.
> x = var('x')
> f = function('f', x)
> g = function('g', x)
> p = f
> print p.substitute_function(f, g) # Outputs "f(x)"
>
>
> # 2. Fails.
> x = var('x')
> f = function('f')
> g = function('g')
> p = f(x)
> print p.substitute_function(f(x), g(x)) # Outputs "f(x)"
>
>
> # 3. Fails.
> x = var('x')
> f = function('f')
> g = function('g')
> p = f(x)
> print p.substitute_function(f, g) # Outputs "g(x)"
>
>
> # 4. Fails.
> x = var('x')
> f = function('f')
> g = function('g')
> p = f(1)
> print p.substitute_function(f(1), g(1)) # Outputs "f(1)"
>
>
> # 5. Works.
> x = var('x')
> f = function('f')
> g = function('g')
> p = f(1)
> print p.substitute_function(f, g) # Outputs "g(1)"
>
>
> # 6. Fails.
> x = var('x')
> f = function('f', x)
> g = function('g', x)
> p = f.diff()
> print p.substitute_function(f, g) # Outputs "D[0](f)(x)"
>
>
> # 7. Fails.
> x = var('x')
> f = function('f', x)
> g = function('g', x)
> p = f.diff()
> print p.substitute_function(f(x), g(x)) # Outputs "D[0](f)(x)"
>
>
> # 8. Works.
> x = var('x')
> f = function('f')
> g = function('g')
> p = f(x).diff()
> print p.substitute_function(f, g) # Outputs "D[0](g)(x)"
>
>
> # 9. Fails.
> x = var('x')
> f = function('f')
> g = function('g')
> p = f(x).diff()(1)
> print p.substitute_function(f(x).diff(), g(x).diff()) # Outputs
> "D[0](f)(1)"
>
>
> # 10. Fails.
> x = var('x')
> f = function('f')
> g = function('g')
> p = f(x).diff()(1)
> print p.substitute_function(f, g) # Crashes.
> }}}
New description:
I'm working on polynomial interpolation at the moment, and these are
starting to hurt. Most of them have workarounds, but there don't seem to
be any for the expressions involving derivatives.
I've also tried with subs() and the like, but one step at a time.
{{{
from sage.all import *
# 1. Fails.
x = var('x')
f = function('f', x)
g = function('g', x)
p = f
print p.substitute_function(f, g) # Outputs "f(x)"
# 2. Fails.
x = var('x')
f = function('f')
g = function('g')
p = f(x)
print p.substitute_function(f(x), g(x)) # Outputs "f(x)"
# 3. Works.
x = var('x')
f = function('f')
g = function('g')
p = f(x)
print p.substitute_function(f, g) # Outputs "g(x)"
# 4. Fails.
x = var('x')
f = function('f')
g = function('g')
p = f(1)
print p.substitute_function(f(1), g(1)) # Outputs "f(1)"
# 5. Works.
x = var('x')
f = function('f')
g = function('g')
p = f(1)
print p.substitute_function(f, g) # Outputs "g(1)"
# 6. Fails.
x = var('x')
f = function('f', x)
g = function('g', x)
p = f.diff()
print p.substitute_function(f, g) # Outputs "D[0](f)(x)"
# 7. Fails.
x = var('x')
f = function('f', x)
g = function('g', x)
p = f.diff()
print p.substitute_function(f(x), g(x)) # Outputs "D[0](f)(x)"
# 8. Works.
x = var('x')
f = function('f')
g = function('g')
p = f(x).diff()
print p.substitute_function(f, g) # Outputs "D[0](g)(x)"
# 9. Fails.
x = var('x')
f = function('f')
g = function('g')
p = f(x).diff()(1)
print p.substitute_function(f(x).diff(), g(x).diff()) # Outputs
"D[0](f)(1)"
# 10. Fails.
x = var('x')
f = function('f')
g = function('g')
p = f(x).diff()(1)
print p.substitute_function(f, g) # Works, prints D[0](g)(1).
}}}
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11842#comment:5>
Sage <http://www.sagemath.org>
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