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File: /usr/local/sage-6.10/local/lib/python2.7/site-packages/sage/misc/functional.py
Type: <type ‘function’>
Definition: sum(expression, *args, **kwds)
Docstring:
Returns the symbolic sum \sum_{v = a}^b expression with respect
to the variable v with endpoints a and b.
INPUT:
- expression - a symbolic expression
- v - a variable or variable name
- a - lower endpoint of the sum
- b - upper endpoint of the sum
- algorithm - (default: 'maxima') one of
- 'maxima' - use Maxima (the default)
- 'maple' - (optional) use Maple
- 'mathematica' - (optional) use Mathematica
- 'giac' - (optional) use Giac
EXAMPLES:
sage: k, n = var('k,n')
sage: sum(k, k, 1, n).factor()
1/2*(n + 1)*n
sage: sum(1/k^4, k, 1, oo)
1/90*pi^4
sage: sum(1/k^5, k, 1, oo)
zeta(5)
Warning
This function only works with symbolic expressions. To sum any
other objects like list elements or function return values,
please use python summation, see
http://docs.python.org/library/functions.html#sum
In particular, this does not work:
sage: n = var('n')
sage: list=[1,2,3,4,5]
sage: sum(list[n],n,0,3)
Traceback (click to the left of this block for traceback)
...
File: /usr/local/sage-6.10/local/lib/python2.7/site-packages/sage/misc/functional.py
Type: <type ‘function’>
Definition: sum(expression, *args, **kwds)
Docstring:
Returns the symbolic sum \sum_{v = a}^b expression with respect
to the variable v with endpoints a and b.
INPUT:
- expression - a symbolic expression
- v - a variable or variable name
- a - lower endpoint of the sum
- b - upper endpoint of the sum
- algorithm - (default: 'maxima') one of
- 'maxima' - use Maxima (the default)
- 'maple' - (optional) use Maple
- 'mathematica' - (optional) use Mathematica
- 'giac' - (optional) use Giac
EXAMPLES:
sage: k, n = var('k,n')
sage: sum(k, k, 1, n).factor()
1/2*(n + 1)*n
sage: sum(1/k^4, k, 1, oo)
1/90*pi^4
sage: sum(1/k^5, k, 1, oo)
zeta(5)
Warning
This function only works with symbolic expressions. To sum any
other objects like list elements or function return values,
please use python summation, see
http://docs.python.org/library/functions.html#sum
In particular, this does not work:
sage: n = var('n')
sage: list=[1,2,3,4,5]
sage: sum(list[n],n,0,3)
Traceback (most recent call last):
...
TypeError: unable to convert n to an integer
Use python sum() instead:
sage: sum(list[n] for n in range(4))
10
Also, only a limited number of functions are recognized in symbolic sums:
sage: sum(valuation(n,2),n,1,5)
Traceback (most recent call last):
...
TypeError: unable to convert n to an integer
Again, use python sum():
sage: sum(valuation(n+1,2) for n in range(5))
3
(now back to the Sage sum examples)
A well known binomial identity:
sage: sum(binomial(n,k), k, 0, n)
2^n
The binomial theorem:
sage: x, y = var('x, y')
sage: sum(binomial(n,k) * x^k * y^(n-k), k, 0, n)
(x + y)^n
sage: sum(k * binomial(n, k), k, 1, n)
2^(n - 1)*n
sage: sum((-1)^k*binomial(n,k), k, 0, n)
0
sage: sum(2^(-k)/(k*(k+1)), k, 1, oo)
-log(2) + 1
Another binomial identity (trac ticket #7952):
sage: t,k,i = var('t,k,i')
sage: sum(binomial(i+t,t),i,0,k)
binomial(k + t + 1, t + 1)
Summing a hypergeometric term:
sage: sum(binomial(n, k) * factorial(k) / factorial(n+1+k), k, 0, n)
1/2*sqrt(pi)/factorial(n + 1/2)
We check a well known identity:
sage: bool(sum(k^3, k, 1, n) == sum(k, k, 1, n)^2)
True
A geometric sum:
sage: a, q = var('a, q')
sage: sum(a*q^k, k, 0, n)
(a*q^(n + 1) - a)/(q - 1)
The geometric series:
sage: assume(abs(q) < 1)
sage: sum(a*q^k, k, 0, oo)
-a/(q - 1)
A divergent geometric series. Don’t forget
to forget your assumptions:
sage: forget()
sage: assume(q > 1)
sage: sum(a*q^k, k, 0, oo)
Traceback (most recent call last):
...
ValueError: Sum is divergent.
This summation only Mathematica can perform:
sage: sum(1/(1+k^2), k, -oo, oo, algorithm = 'mathematica') # optional - mathematica
pi*coth(pi)
Use Maple as a backend for summation:
sage: sum(binomial(n,k)*x^k, k, 0, n, algorithm = 'maple') # optional - maple
(x + 1)^n
Python ints should work as limits of summation (trac ticket #9393):
sage: sum(x, x, 1r, 5r)
15
Note
- Sage can currently only understand a subset of the output of Maxima, Maple and
Mathematica, so even if the chosen backend can perform the summation the
result might not be convertable into a Sage expression.
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