In sage 3.x, I used the below function to automatically substitute into an expression all assignments I have made previously. How can I get it to work in Sage 5.x or is there a better way now?
def subsg(variable, *args):
"""
Substitutes all definitions in the global name space for the variables contained in 'variable' and returns the result.
INPUT:
variable -- a symbolic variable
*args -- an optional dictionary containing additional parameter definitions
EXAMPLE:
sage: var ('a b c d')
a b c
sage: f = a*x
sage: a = 2*b
sage: b = c^2
sage: cons1 = dict(c = d^3)
sage: subsg(f,cons1)
2*d^6*x
Or, if cons1 is not to be used:
sage: subsg(f)
2*c^2*x
"""
expr1 = variable
expr2 = variable.subs(globals()).subs(*args)
while expr1 <> expr2:
expr1 = expr2
expr2 = expr1.subs(globals()).subs(*args)
return expr1
