how to make sum of (for loop)

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Mech
Mech 2014-6-7
回答： David Sanchez 2014-6-9
I need for loop or any method to calculat next sum
  • m=1:n
  • a+2(cos(b))
  • a+2(cos(b)+cos(2b))
  • a+2(cos(b)+cos(2b)+cos(3b))
  • a+2(cos(b)+cos(2b)+.............cos(nb))
  2 个评论
Cedric
Cedric 2014-6-7
What have you done/tried so far?
Mech
Mech 2014-6-7
编辑：Mech 2014-6-7
ok
  • a1=a+2(cos(b))
  • a2=a+2(cos(b)+cos(2b))
  • a3=a+2(cos(b)+cos(2b)+cos(3b))
I need value of a1,a2,a3

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回答（3 个）

Roger Stafford
Roger Stafford 2014-6-7
编辑：Roger Stafford 2014-6-7
Assuming b is a scalar,
s = a + 2*sum(cos((1:n)*b));
An alternate formula without the long summation is:
s = a + 2*cos((n+1)*b/2)*sin(n*b/2)/sin(b/2);
Mech
Mech 2014-6-8
help guys :(
David Sanchez
David Sanchez 2014-6-9
the for loop:
a = 3; % or whatever value you have in mind
b = 2; % or whatever value you have in mind
n = 10; % or whatever value you have in mind
your_sum = 0; % initialization of summation part
for m=1:n
your_sum = your_sum + cos(m*b);
end
your_sum = a + 2*your_sum;

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