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For loops: initialize the sum variable

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Abida Islam
Abida Islam 2019 年 12 月 9 日
Answered: Walter Roberson 2019 年 12 月 9 日
For this code if put the initial value of sum=1 then I get different answer.But I thought the inital values of sum doesn't matter? Can anyone explain?
m = input('Please enter the number of terms in the sum: ');
n = 0;
SUM = 0;
disp(' ')
for n = 1:m
an = (-1/3)^n/(2*n + 1);
SUM = SUM + an = (-1/3)^n/(2*n + 1);
Val_Exp = sqrt(12)*SUM;
Prec_pi = abs(pi-Val_Exp);
fprintf('For n = %2i, Value = %.15f to a precision of %.10e.\n', n, Val_Exp, Prec_pi)
end disp(' ')

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Walter Roberson
Walter Roberson 2019 年 12 月 9 日
SUM = SUM + an = (-1/3)^n/(2*n + 1);
That is invalid syntax. You cannot have two = in the same statement.
end disp(' ')
That is invalid syntax. You need a statement separator between end and what follows.
Why whould you think that the initial values did not matter?
I would suggest to you that what you missed is that your summation is really over 0 to m instead of 1 to m, and that there are two ways you can compute that: you can either initialize the sum to 0 and loop from 0, or you can initialize the sum to 1 and loop from 1. Either way works because the term for n = 0 works out to 1.

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