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2012-08-26 18:31:51 +0200	marked best answer	Noob question about lists in sum() You can always do `sage: dings = [1 , 2, 3, 4, 5] sage: length = len(dings) sage: sum([1/dings[k] for k in range(length)])` or `sage: var('k') sage: d(k) = 1/k # defines d to be a (symbolic) function sage: sum(d(k), k, 1, 5)` The second version works more generally: `sage: var('k') sage: d(k) = 1/k^2 sage: sum(d(k), k, 1, infinity) 1/6*pi^2`
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2012-08-26 18:16:16 +0200	commented answer	Noob question about lists in sum() Me idiot! It sure does! I just somehow ... didn't recognize that on my first read. So thx you two and sry for wasting your time by being temporarily illiterate.
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2012-08-26 14:50:47 +0200	answered a question	Noob question about lists in sum() [edit]My following answer is dumb due to not properly reading the first answer[/edit] Thanks for your answer! The thing is that I actually want to use a list of measured values, so dings would not be a list of following integers (like range(1,5)), but some (real) numbers, for example dings = [1.2438, 1.2473, 1.2398] just with more than 3 numbers. So I do need to use a list in a sum context. I could write it with a for loop (and did, which worked), but I really want to use a sum.
2012-08-26 12:48:00 +0200	asked a question	Noob question about lists in sum() Hi there, I have a (presumably) very easy question: `var('k') sum(1/k, k, 1, 5)` works, but `dings = [1 , 2, 3, 4, 5] length = len(dings) sum(1/dings[k], k, 0, length - 1)` does not. Error Message: Traceback (most recent call last): File "<stdin>", line 1, in <module> File "_sage_input_6.py", line 10, in <module> exec compile(u'open("___code___.py","w").write("# -- coding: utf-8 --\\n" + _support_.preparse_worksheet_cell(base64.b64decode("ZGluZ3MgPSBbMSAsIDIsIDMsIDQsIDVdCmxlbmd0aCA9IGxlbihkaW5ncykKc3VtKDEvZGluZ3Nba10sIGssIDAsIGxlbmd0aCAtMSAp"),globals())+"\\n"); execfile(os.path.abspath("___code___.py")) File "", line 1, in <module> File "/tmp/tmpDDv20Z/___code___.py", line 5, in <module> exec compile(u'sum(_sage_const_1 /dings[k], k, _sage_const_0 , length -_sage_const_1 ) File "", line 1, in <module> File "expression.pyx", line 4163, in sage.symbolic.expression.Expression.__index__ (sage/symbolic/expression.cpp:20198) File "expression.pyx", line 745, in sage.symbolic.expression.Expression._integer_ (sage/symbolic/expression.cpp:5152) TypeError: unable to convert x (=k) to an integer So I tried writing it with dings[int(k)], didn't work either. Why? Thanks!