Get assumptions by variables

[sagetrac-noud]

Hi everyone,

I'm very exited to create my first ticket and add my first patch. It would be nice if the assumption function could return the assumptions of a variable explicitly. For example:

sage: x, y, z = var('x y z')
sage: assume(x, 'integer')
sage: assume(y > 0)
sage: assume(y**2 + z**2 == 1)
sage: assume(x < 0)
sage: assumptions()
[x is integer, y > 0, y^2 + z^2 == 1, x < 0]
sage: assumptions(x)
['integer', x < 0]
sage: assumptions(x, y)
[x is integer, x < 0, y > 0, y^2 + z^2 == 1]
sage: assumptions(z)   
[y^2 + z^2 == 1]

I'll upload a solution for this suggestion shortly.

Apply: attachment: trac_13708_get_assumption_by_variables.patch, attachment: trac_13708-eliminate_strings.patch

Component: symbolics

Keywords: symbolic, assumptions, variable

Author: Noud Aldenhoven, Burcin Erocal

Reviewer: Burcin Erocal, Noud Aldenhoven

Merged: sage-5.6.beta1

Issue created by migration from https://trac.sagemath.org/ticket/13708

[sagetrac-noud]

Attachment: trac_13708_get_assumption_by_variables.patch.gz

[sagetrac-noud]

comment:2

I added a patch which allows sage to do the things shown in the Description box. I hope this code makes sense. Please be easy on me, it's my first patch. ;)

Best,
Noud

[burcin]

Author: Noud Aldenhoven, Burcin Erocal

[burcin]

Reviewer: Burcin Erocal

[burcin]

comment:4

Attachment: trac_13708-eliminate_strings.patch.gz

Thanks for the patch. Your changes look good to me. I attached a referee patch to fix some minor issues:

• do not use strings to check if an assumption contains a variable
• minor documentation fix (code blocks should be preceeded by ::)

If you're OK with my changes, feel free to switch this ticket to positive_review.

[sagetrac-noud]

comment:6

Thank you, this seems very nice. I like it.

However I would still like to do something like this:

sage: x = var('x')
sage: assume(x, 'integer')
sage: 'integer' in assumptions(x) # or something in this fashion
True

That's why I added a 'integer' string in the assumption code, but I see that you removed this in the newer patch. I still do not know a nice solution for this (small) problem.

[burcin]

comment:7

Replying to @sagetrac-noud:

Thank you, this seems very nice. I like it.

However I would still like to do something like this:

sage: x = var('x')
sage: assume(x, 'integer')
sage: 'integer' in assumptions(x) # or something in this fashion
True

That's why I added a 'integer' string in the assumption code, but I see that you removed this in the newer patch. I still do not know a nice solution for this (small) problem.

I removed that code because treating only the integer case specially is not a good long term solution.

The right way to handle this is via the is_integer() method of symbolic expressions:

sage: var('y', domain=ZZ)
y
sage: y.is_integer()
False
sage: var('a')
a
sage: a.is_integer()
False

Unfortunately, our wrappers around Maxima assumptions don't know anything about these and these don't know about Maxima assumptions. I can't even find a bug to make the two work together. Would you be interested in helping out?

In order to make assumptions set domains in Pynac, all we need to do is add a call to SR.symbol(variable_name, domain=new_domain) in the code for assume() and reset the domain to CC in forget().

This should all be done on a separate ticket of course.

[burcin]

Changed reviewer from Burcin Erocal to Burcin Erocal, Noud Aldenhoven

[sagetrac-noud]

comment:8

Replying to @burcin:

The right way to handle this is via the is_integer() method of symbolic expressions:

sage: var('y', domain=ZZ)
y
sage: y.is_integer()
False
sage: var('a')
a
sage: a.is_integer()
False

Unfortunately, our wrappers around Maxima assumptions don't know anything about these and these don't know about Maxima assumptions. I can't even find a bug to make the two work together. Would you be interested in helping out?

Certainly I would like to help! But I have no idea how to approach. To me it looks like if the function is_integer() should be modified. Could you explain to me a bit better how this works? I also don't get how this should work with SR.symbol.

[sagetrac-robert-dodier]

comment:10

You can ask Maxima to report what it assumptions it has recorded for a variable, via facts(x) where x is the variable of interest. Also, propvars(p) returns the variables for which property p has been declared, e.g. propvars('integer). I'm guessing that it might be preferable to get the report directly from Maxima since that's what actually affects results. Hope this helps.

[jdemeyer]

Merged: sage-5.6.beta1