Hi,
I'm wondering why the next code doesn't work as intended:
myMin(x,y) = min(x,y)
print myMin(3,2)
3
However:
print min(3,2)
2
In fact, Sage says that the function myMin is (x, y) |--> x. Why is this? Is there a way I could use min in a symbolic expression?
Well, min is not what we call a symbolic function. Since x is earlier in the lexicographic order than y:
sage: var('y')
y
sage: min(x,y)
x
We work around that like this.
sage: f(x,y) = 2*min_symbolic(x,y)
sage: f(3,2)
4
sage: f(2,3)
4
This should probably be easier to find...
You can at least do it in another way:
sage: def myMin(x,y):
....: return min(x,y)
....:
sage: print myMin(3,2)
2
But concerning your original post, it really looks like a bug. I am not expert enough. If it is indeed a bug, we should report it.
You can also use a lambda function:
f = lambda x,y: min(x,y)
print f(4,3)
I don't know much about them except they seem to delay evaluation of the function until you pass it variables. doing
f(x,y) = min(x,y)
doesn't (?)
I believe the key difference is that the lambda function will give you numerical function, not symbolic: "f(x) = sin(x)" and then "diff(f)" will give you "cos(x)", but "g = lambda x: sin(x)" and then "diff(g)" will give you TypeError, cuz the function is no longer symbolic.
Asked: 2012-01-06 12:06:02 +0100
Seen: 1,647 times
Last updated: Jan 06 '12
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