conditions in matlab (for/if/else)

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habib nasta 2018-10-7

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评论： Image Analyst 2018-10-7

Hi, I am trying to create a a function in which I can put in all the numbers from the 100 to 150 and extract all the odd numbers and do the sum square of these numbers I tried using the for function but I don't know how to take it after that

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Answer 1

Image Analyst 2018-10-7

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在 MATLAB Online 中打开

Try this:

% Generate starting signal.
v = 100:150
% Extract indexes of the odd numbers.
oddIndexes = logical(mod(v, 2))
% Extract the odd numbers themselves.
oddNumbers = v(oddIndexes)
% Compute the sum of the squares of odd numbers.
sumOfSuqares = sum(oddNumbers .^ 2)

Hopefully it's not your homework, or else you can't use my code.

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habib nasta 2018-10-7

thank you that was really helpful. It's not my homework actually (I wish it was) but i was wondering if you could show me how is it done using using the conditions like I was thinking that I should run a "for" from 100 to 150 and after that I should put a condition that if it's odd to store its square in a separate variable and after that sum it with the rest of the odd numbers but I am not sure how to tackle it honestly

Image Analyst 2018-10-7

在 MATLAB Online 中打开

That's not the way MATLAB programmers would do it, unless they're a complete beginner coming from an old-school antique language. but nonetheless, here are both ways:

% Generate starting signal.
v = 100:150
% Klunky for loop way:
theSum = 0;
oddNumbers = []; % Initialize to null.
for k = 1 : length(v)
  if rem(v(k), 2) == 1
    % It's odd
    oddNumbers = [oddNumbers, v(k)];
    theSum = theSum + v(k)^2;
  end
end
oddNumbers
theSum
% Much better vectorized way:
% Extract indexes of the odd numbers.
oddIndexes = logical(mod(v, 2))
% Extract the odd numbers themselves.
oddNumbers = v(oddIndexes)
% Compute the sum of the squares of odd numbers.
sumOfSuqares = sum(oddNumbers .^ 2)