# how to sum floating point elements of an array

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Subrat kumar sahoo on 11 Sep 2012
Commented: SWATI BHARGAVA on 2 Dec 2019
Hi I have an array which has floating point inputs. I need to sum all the elements to get a single value. The command 'sum' takes only integer inputs and throws error "??? Subscript indices must either be real positive integers or logicals" for double type inputs. Will appreciate any help.
Thanks, Subrat
##### 2 CommentsShowHide 1 older comment
Yoheena Kotikawatte on 24 Mar 2018
Hi! How do i make this work:
k = 25;
v=[1;0];
pvalues=[0:.01:1];
for i1=1:length(pvalues) p=pvalues(i1); A =[(2-p) (0.25*p); p (1.25-0.25*p)]; numbbacteria=(A^k)*v; y(p) = sum(numbbacteria); end
plot(pvalues,y) ylabel('Total number of bacteria'); xlabel('Probability that a bacteria will switch states');
because I get the eror: Subscript indices must either be real positive integers or logicals.
Error in p_file (line 8) y(p) = sum(numbbacteria);
I do understand the eror but how do i make it work with decimals?

Jan on 11 Sep 2012
Edited: Jan on 11 Sep 2012
While the command sum accepts arrays of floating point types also (see the documention!), this will fail if you overwrite the name "sum" by a variable:
clear sum % The initial status
sum(rand(1,5)) % works!
sum = 1:10; % Brrr, don't do it, although it is not a bug
sum(rand(1,5)) % Bug!
Check overwritten names by the command whos.
SWATI BHARGAVA on 2 Dec 2019
Saved me too! Thank you!! Glad came across this solution!

Oleg Komarov on 11 Sep 2012
"??? Subscript indices must either be real positive integers or logicals"
It means you're doing something:
a = 1:0.1:2;
b = rand(20,1);
b(a)
You cannot select position 1.1, 1.2... of an array (or -1). The indexing of an array is done with whole positive integers 1, 2, 3...
Subrat kumar sahoo on 11 Sep 2012
Thanks Oleg for explaining the error

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