Problem with IF statement

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Fe99 2020-11-27

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https://ww2.mathworks.cn/matlabcentral/answers/665578-problem-with-if-statement

评论： Rik 2020-11-27

why doesn't it give me a result if I enter " if D == l " I wan't to calculate all initial velocities and angles at which the length is 100m.

clear all
close all
clc
%1
v0 = [15:0.001:60]; %initial velocity
kot = [15:60]; %angle
g = 9.81; %gravity
l = 100; %distance
for i = 1:length(v0)
    for j = 1:length(kot)
        D = (v0(i)^2*sind(2*kot(j)))/g; %distance
        if D == l
            fprintf('Vo = %.2f m/s | kot = %.2f° | D = %.2f  \n',v0(i),kot(j), D);
        end
    end
end

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回答（1 个）

Rik 2020-11-27

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/665578-problem-with-if-statement#answer_558098

Don't use clear all. You don't need it.

I suspect you encountered the wondrous world of floats. Computers don't have infinite memory and may round numbers in ways that you don't expect. This is especially a problem if you are asking for exact equality, while you would be satisfied with equality within machine precision.

Instead of a==b use abs(a-b)<tol. You can use the eps function, or set another value.

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Fe99 2020-11-27

sorry my bad. thanks for answer

Rik 2020-11-27

No problem. If my answer solved your question, please consider marking my answer as accepted answer. If not, feel free to comment with your remaining issues.

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