Need help with plotting a complicated for loop

Question

Anthony Schmidt 2020-4-2

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/514947-need-help-with-plotting-a-complicated-for-loop

评论： David Hill 2020-4-3

采纳的回答： David Hill

在 MATLAB Online 中打开

Create a function called f that receives an input vector and satisfies the following criteria:

For values of x > 2, f(x) = x^2

For values of x ≤ 2, f(x) = 2x

Plot your results for values of x from –3 to 5. The plot should have a title, and both the x and y axis should be labeled.

I've got my function written and it works, but when I run it, it only plots values for when f(x)=x^2. I know I have a small mistake somewhere, and I'd appreciate if someone could help me out. Here's what I've got so far:

function y=f(x)
    for i=x
            if i>2
                y=x.^2;
            elseif i<=2
                y=2*x;
            end
    end
    xlabel 'x'
    ylabel 'f(x)'
    title('Unit Example 4, Problem 6')
    plot(x,y,'k*')
end

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Answer 1

David Hill 2020-4-3

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/514947-need-help-with-plotting-a-complicated-for-loop#answer_423697

在 MATLAB Online 中打开

function y=f(x)
    for i=x
            if i>2
                y=x.^2;%you are reassigning y every iteration, your y will be the last one
            elseif i<=2
                y=2*x;
            end
    end
    xlabel 'x'
    ylabel 'f(x)'
    title('Unit Exam 4, Problem 6')
    plot(x,y,'k*')
end

It is actually much easier without a for-loop.

function y=f(x)
y=zeros(size(x));
y(x>2)=x(x>2).^2;
y(x<=2)=x(x<=2)*2;
xlabel 'x'
ylabel 'f(x)'
title('Unit Exam 4, Problem 6')
plot(x,y,'k*')
end

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Anthony Schmidt 2020-4-3

Your funtion works properly and shows the correct values and figure, but question I posted is intending on the user utililzing for/while loops.

David Hill 2020-4-3

在 MATLAB Online 中打开

function y=f(x)
    for i=1:length(x)
            if x(i)>2
                y(i)=x(i)^2;
            else
                y(i)=2*x(i);
            end
    end
    xlabel 'x'
    ylabel 'f(x)'
    title('Unit Exam 4, Problem 6')
    plot(x,y,'k*')
end