add `force` to `to_cnf` and `to_dnf`; `is_literal` made more general #18912

smichr · 2020-03-20T00:18:12Z

References to other Issues or PRs

Brief description of what is fixed or changed

When to_cnf is given an expression with more than 8 variables and simplify=True it will not simplify the expression -- and may not return it in cnf form and does so silently. Now, a ValueError is raised if simplification is requested and force is not True. The user has the option to not use simplify or to use force.

In addition, is_literal and is_a_literal were combined and made to recognize that things like x < 2 can be treated like a literal. This fixes issue 9949.

Finally, a quick-exit is given to simplify_logic to deal with trivial cases that don't need simplification and are already in the correct, most implified form.

Other comments

Release Notes

logic
- boolalg
  - to_cnf/to_dnf (when simplify=True) require force=True` if there are more than 8 variables
  - simplify_logic recognizes trivial simplified cases
  - is_literal can treat Not as literal or not by using the literal_Not flag

sympy-bot · 2020-03-20T00:18:22Z

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logic
- boolalg (#18912 by @smichr)
- to_cnf/to_dnf (when simplify=True) require force=True` if there are more than 8 variables (#18912 by @smichr)
- simplify_logic recognizes trivial simplified cases (#18912 by @smichr)
- is_literal can treat Not as literal or not by using the literal_Not flag (#18912 by @smichr)

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#### References to other Issues or PRs
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fixes #9949
fixes #18904

#### Brief description of what is fixed or changed

When `to_cnf` is given an expression with more than 8 variables and `simplify=True` it will not simplify the expression -- and may not return it in cnf form and does so silently. Now, a ValueError is raised if simplification is requested and `force` is not True. The user has the option to not use `simplify` or to use `force`.

In addition, `is_literal` and `is_a_literal` were combined and made to recognize that things like `x < 2` can be treated like a literal. This fixes issue 9949.

Finally, a quick-exit is given to `simplify_logic` to deal with trivial cases that don't need simplification and are already in the correct, most implified form.

#### Other comments


#### Release Notes

<!-- Write the release notes for this release below. See
https://github.com/sympy/sympy/wiki/Writing-Release-Notes for more information
on how to write release notes. The bot will check your release notes
automatically to see if they are formatted correctly. -->

<!-- BEGIN RELEASE NOTES -->
* logic
    * boolalg
        * `to_cnf`/`to_dnf` (when `simplify=True) require `force=True` if there are more than 8 variables
        * `simplify_logic` recognizes trivial simplified cases
        * `is_literal` can treat `Not` as literal or not by using the `literal_Not` flag
<!-- END RELEASE NOTES -->

Update

The release notes on the wiki have been updated.

codecov · 2020-03-20T01:38:05Z

Codecov Report

Merging #18912 into master will increase coverage by 0.031%.
The diff coverage is 90.476%.

@@              Coverage Diff              @@
##            master    #18912       +/-   ##
=============================================
+ Coverage   75.648%   75.679%   +0.031%     
=============================================
  Files          647       647               
  Lines       168520    168535       +15     
  Branches     39710     39713        +3     
=============================================
+ Hits        127483    127547       +64     
+ Misses       35476     35439       -37     
+ Partials      5561      5549       -12

asmeurer · 2020-03-20T02:02:58Z

What is the motivation for the literal_Not flag? The inclusion of Not is based on a standard definition of "literal".

smichr · 2020-03-20T10:50:13Z

What is the motivation for the literal_Not flag

Hmm...I must have had a different problem when trying to detect the quick exit case for simplify_logic. When I retested now, everything passed. Let's see if the full suite raises any objections...

smichr · 2020-03-20T12:37:31Z

sympy/logic/boolalg.py

@@ -2782,6 +2793,16 @@ def simplify_logic(expr, form=None, deep=True, force=False):
    if form not in (None, 'cnf', 'dnf'):
        raise ValueError("form can be cnf or dnf only")
    expr = sympify(expr)
+    # check for quick exit: right form and all args are


reviewer: please check to see that this is the right logic for quick exit: if an expression is in the right form and all args are literal then there is nothing left to do.

smichr · 2020-03-20T12:38:16Z

sympy/logic/boolalg.py

+        return expr.args[0].is_Atom
+    elif expr in (True, False) or expr.is_Atom:
+        return True
+    elif not isinstance(expr, BooleanFunction) and all(


e.g. x < 3 is treated like a literal but x + y < 3 would not be a literal.

sympy/logic/boolalg.py

smichr added 4 commits March 19, 2020 11:52

9949: recognize literal relationals

7893df7

require force w/ to_(cnf|dnf) when using simplify

be5aa31

nonBoolean with literal args->literal

8e10420

Not as literal or not

7f6db1c

remove literal_Not

e2d96cc

remove all use of literal_Not

b7b90fd

smichr commented Mar 20, 2020

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Update test_boolalg.py

a315594

smichr commented Mar 20, 2020

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smichr added the PR: sympy's turn label Mar 20, 2020

smichr merged commit acca306 into sympy:master Mar 21, 2020

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add `force` to `to_cnf` and `to_dnf`; `is_literal` made more general #18912

add `force` to `to_cnf` and `to_dnf`; `is_literal` made more general #18912

smichr commented Mar 20, 2020

sympy-bot commented Mar 20, 2020 •

edited

codecov bot commented Mar 20, 2020 •

edited

asmeurer commented Mar 20, 2020

smichr commented Mar 20, 2020

smichr Mar 20, 2020

smichr Mar 20, 2020 •

edited

add force to to_cnf and to_dnf; is_literal made more general #18912

add force to to_cnf and to_dnf; is_literal made more general #18912

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smichr commented Mar 20, 2020

References to other Issues or PRs

Brief description of what is fixed or changed

Other comments

Release Notes

sympy-bot commented Mar 20, 2020 • edited

codecov bot commented Mar 20, 2020 • edited

Codecov Report

asmeurer commented Mar 20, 2020

smichr commented Mar 20, 2020

smichr Mar 20, 2020

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add `force` to `to_cnf` and `to_dnf`; `is_literal` made more general #18912

add `force` to `to_cnf` and `to_dnf`; `is_literal` made more general #18912

sympy-bot commented Mar 20, 2020 •

edited

codecov bot commented Mar 20, 2020 •

edited

smichr Mar 20, 2020 •

edited