Doubt in a product erro

Question

Nélio Dias 2021-4-2

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评论： Sulaymon Eshkabilov 2021-4-4

采纳的回答： Sulaymon Eshkabilov

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Hi, I have wrinting a code e get a 1×0 empty double row vector error

So, what I wrote:

t1 = 0:0.01:300;
pmenor = 25*0.9;
pmaior = 25*(1.1);
idx1 = find(t1== pmenor);
idx2 = find(t1 == pmaior);

I got

idx2 =
  1×0 empty double row vector

But, if I write:

  idx2 = find(t1 == 27.5);
  
  idx2 =
        2751

So I dont understand the error since idx1 gives me the correct answer, because we know that 25*1.1 = 27.5.

Thanks for reading.

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Answer 1

Sulaymon Eshkabilov 2021-4-2

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编辑：Sulaymon Eshkabilov 2021-4-2

在 MATLAB Online 中打开

Here is a small correction to obtain the correct answers in your exercise:

t1 = 0:0.01:300;
N = 2;                % Number of decimal digits to be rounded, e.g.: N = 2 or 3 or 5, etc. 
pmenor = round(25*0.9, N);
pmaior = round(25*(1.1), N);
idx1 = find(t1== pmenor);
idx2 = find(t1 == pmaior);

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Nélio Dias 2021-4-4

Thanks for the help.

Sulaymon Eshkabilov 2021-4-4

You are welcome - it is a pleasure.

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Answer 2

the cyclist 2021-4-2

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https://ww2.mathworks.cn/matlabcentral/answers/791254-doubt-in-a-product-erro#answer_665574

The reason has to do with the accuracy of floating-point math on a binary computer. I suggest you read this question and answer, to get a better understanding of what is going on.