On Jan 16, 5:53 pm, Ed Scheinerman <edward.scheiner...@gmail.com>
wrote:
> I'm confused by the fact that variables defined inside functions can
> "leak out" and become global variables. Here's what I've noticed.
The problem is twith the function var. According to its documentation:
(var?)
"The new variable is both returned and automatically injected
into the global namespace. If you need symbolic variable in
library code, it is better to use either SR.var() or SR.symbol()."
The var function is only intended to be used on an interactive session
by the user. If you need variables inside a function you need SR.var
def steiner(a,b,c):
"""
Given three points in the plane, find the point p that minimizes
the sum of the distances to those three points.
"""
x = SR.var('x')
y = SR.var('y')
p = (x,y) # unknown point
# objective function to minimize
obj = dist(p,a) + dist(p,b) + dist(p,c)
# start search at center of mass of the three points
p0 = ( (a[0]+b[0]+c[0])/3., (a[1]+b[1]+c[1])/3. )
print "Starting optimiztion at", p0
print obj.subs(x=p0[0], y=p0[1])
return minimize(obj,p0)
Then:
sage: x = [1,2,3]
sage: y = [4,5,6]
sage: x
[1, 2, 3]
sage: y
[4, 5, 6]
sage: steiner((1,1), (2,3), (5,2))
Starting optimiztion at (2.6666666666666665, 2.0)
5.4788343901030965
Optimization terminated successfully.
Current function value: 5.303240
Iterations: 6
Function evaluations: 7
Gradient evaluations: 7
(2.20179756615, 2.46316721759)
sage: x
[1, 2, 3]
sage: y
[4, 5, 6]
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