Why am I not getting a vector output?

Question

Dawid Brits 2019-10-17

0
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https://ww2.mathworks.cn/matlabcentral/answers/485785-why-am-i-not-getting-a-vector-output

评论： Dawid Brits 2019-10-17

Hi All,

Ive writen this function that computes the gradient vector for a function, but it only gives me a single value output. What am I doing wrong?

gradlandscape(3, 3);
function [retx, rety] = gradlandscape(x, y)
h = 0.1;
retx = (landscape(x+h, y)-landscape(x-h, y))/(2*h);
rety = (landscape(x, y+h)-landscape(x, y-h))/(2*h);
 
    function M = landscape(x, y)
       M = H1(x, y) + H2(x, y);
       
        function h1 = H1(x, y)
            R1 = 2;
            s1 = [-2;2];
            n1 = 2;
       h1 = (1./(1+(R1./sqrt((x-s1(1)).^2+(y(:)-s1(2)).^2)).^n1));
        end
        function h2 = H2(x, y)
            R2 = 1;
            s2 = [3;-1];
            n2 = 1;
       h2 = (1./(1+(R2./sqrt((x-s2(1)).^2+(y(:)-s2(2)).^2)).^n2));
        end
    end
end

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Answer 1

Adam Danz 2019-10-17

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https://ww2.mathworks.cn/matlabcentral/answers/485785-why-am-i-not-getting-a-vector-output#answer_396715

编辑：Adam Danz 2019-10-17

That's because you're only asking for a single output (by default). If you want both outputs, you must include two outputs in your call to the function.

[retx, rety] = gradlandscape(3, 3)

If the intention of the function was to produce a single output that is a 1 x 2 vector instead of two scalar outputs, then you'll need to change the function like this:

function retxy = gradlandscape(x, y)
h = 0.1;
retxy(1) = (landscape(x+h, y)-landscape(x-h, y))/(2*h);
retxy(2) = (landscape(x, y+h)-landscape(x, y-h))/(2*h);
.
.
.