Problem: We want to calculate the sum of the elements of a list of numbers. Suppose this list is named l and has been assigned the value {1,2, ..., 20}
Method 1: ( Use the Mathematica function to total the values in a list. )
Total[l]
Method 2: ( Use the formula for the sum of an arithmetic sequence, with l[[1]] being the first element, l[[Length[l]]] being the last element and Length[l] the number of elements.)
(l[[1]] + l[[Length[l]]])*Length[l]/2
Method 3: ( Go through all the elements from the first to the last and add them to a running total. )
Sum[l[[k]], {k, 1, Length[l]}]
Method 4: ( Recursively define the total of a list. )
s[{}] := 0
s[l_] := First[l] + s[Rest[l]]
Method 5: ( Use some intricate method of the Mathematica language. )
Fold[#1 + #2 &, 0, l]
All five methods give the same result 210.
Set l := Array[#&,20];
Or use the following to test the commands.
Total[Array[#&,20]]
(Array[#&,20][[1]] + Array[#&,20][[Length[Array[#&,20]]]])*Length[Array[#&,20]]/2
Sum[Array[#&,20][[k]], {k, 1, Length[Array[#&,20]]}]
s[{}] := 0
s[l_] := First[l] + s[Rest[l]]
s[Array[#&,20]]
Fold[#1 + #2 &, 0, Array[#&,20]]
Notes on Blackbody radiation
2 years ago
I have a list, how can i sum it using sumation? I didn't understand with your example. This is what i'm trying to do.
ReplyDeleter := RandomReal[{-10, 10}];
s = {};
x = 1; While[x <= 1000, AppendTo[s, r]; x++]
ListLinePlot[s]
Total[s]
c = Count[s, _]
Take[s, 1]
You are not building a list.
ReplyDeleteYou should have done s = AppendTo[s, r]
Go to http://stackoverflow.com/ for expert answers on Mathematica and other computer languages.
trying to work my way around this but makes my head spin...urrgh. But thumbs up for the detailed explanation though. Think I will head over to Wollfram Alpha :)
ReplyDelete