How writing code sum 1+2+3+4+...+n

Hi. How I can writing code in MATLAB sum 1+2+3+4+..+n

and I can change ( n ) to any numbers and MATLAB can sum for me.

Thank you

Answer 1

[Jos (10584)]

or know your math classics ...

n = 120345428372
s = n*(n+1)/2
% sum(1:n) will fail!

[James Tursa]

Well, n*(n+1)/2 fails also ...

>> n = 120345428372;
>> fprintf("%20f\n",n*(n+1)/2)
7241511065080263868416.000000
>> vpa(n)*vpa(n+1)/2
ans =
7241511065080263999378.0

[Jos (10584)]

So true, James :-D

[Walter Roberson]

n = 120345428372;
sym(n) * (sym(n)+1) / 2

ans = 

7241511065080263999378

syms m
symsum(m, 1, n)

ans = 

7241511065080263999378

[Alexander]

Maybe a stupid question, but what is the right answer? 7241511065080263999378 or 7241511065080263868416?

[Walter Roberson]

v = sym('7241511065080263999378')

v = 

7241511065080263999378

fprintf('%.999g\n', double(v))

7241511065080263868416

So 7241511065080263868416 is the closest double precision representation of 7241511065080263999378

eps(double(v))

ans = 1048576

which is large enough adjacent representable double precision numbers in that range are 1048576 apart.

[Alexander]

Understood. Thank you

Answer 2

[Stephan]

n = 4;  
A = sum(1:n)

[M Ahasanul]

10