Evaluating a symbolic expression for a Graph
 
  
 
  
 
 
 
 
 
 
    
        
        asked 12 years ago  
 
 patronics gravatar image  
 
 
 
 
    
        
        updated 12 years ago  
 
 
 
 
 
I'm able to do this:
 
sage: f = function('radius', nargs=1, evalf_func=Graph.radius)
sage: f(graphs.HouseGraph())
2
 
But not this:
 
sage: var('G')
sage: expr = f(G)
sage: expr.subs(G=graphs.HouseGraph())
...
TypeError: no canonical coercion from <class 'sage.graphs.graph.Graph'> to Symbolic Ring
 
What am I missing? Is it not possible to use symbolic expressions like this?
 
Preview: (hide)
 
 
 
 
          
 
Comments
The substitution is implemented in the stricter "sense of algebra". The instance expr is namely
sage: expr.__class__
<type 'sage.symbolic.expression.Expression'>

sage: expr
radius(G)

sage: expr.__dict__
<dictproxy {'__doc__': None,
 '__module__': 'sage.categories.commutative_rings',
 '_reduction': (<built-in function getattr>,
  (Category of commutative rings, 'element_class')),
 '_sage_src_lines_': <staticmethod object at 0x7f28c20399b8>}>

sage: expr.subs??
(Python allows better ways to call a known function on a known argument, and explicit is better then implicit. Why this contorsion by subs?)
dan_fulea gravatar imagedan_fulea (
    
        7 years ago
    )
add a comment