Solving a system of inequalities using an eigenfunction and if, else.

Question

Sandra 2023-6-8

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https://ww2.mathworks.cn/matlabcentral/answers/1980234-solving-a-system-of-inequalities-using-an-eigenfunction-and-if-else

评论： Dyuman Joshi 2023-6-8

采纳的回答： Alan Stevens

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Hi, I have a task to do, but something is wrong here.

What I need to do: Make and test function for x=1,...,10, f(x) is in photo, and make a plot for it.

This is what I done:

function [y]=Zad1_3(x)
 r1=x^2-2;x;
 r2=5,x;
 r3=x+3,x;
for x = 1:10
    if (r1<0)
        y=x^2-2,x
    elseif (r2==0)
        y=5,x
    elseif (r3>0)
        y=x+3,x
    end
end

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Dyuman Joshi 2023-6-8

I don't understand why you have put x after r1, r2, and r3 and in if-else statements.

And why create an extra variable when you can directly compare x according to the conditions?

Also, when you use x as the index for for loop, you overwrite the input that was provided to the function. And the final output y will correspond to x = 10, regardless of what you will input.

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Answer 1

Alan Stevens 2023-6-8

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https://ww2.mathworks.cn/matlabcentral/answers/1980234-solving-a-system-of-inequalities-using-an-eigenfunction-and-if-else#answer_1252659

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Your function needs to be more like this, for example. Set values of x outside the function, call the function with these values, assign the results to y (say) and plot(x,y)

function f = Zad1_3(x)
        for i = 1:numel(x)
             if x(i) < 0
                 f(i) = x(i).^2 - 2;
             elseif x(i) == 0
                 f(i) = 5;
             else
                 f(i) = x(i) + 3;
             end
        end
end