Element wise conditional evaluation of a function over a meshgrid

Question

Adamya Goyal 2020-4-9

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/516778-element-wise-conditional-evaluation-of-a-function-over-a-meshgrid

评论： James Browne 2020-4-10

I created a 2-D mesh using meshgrid. Now, I want to evaluate a function over this mesh based on the elements of mesh i.e., if the mesh elements are equal then evaluate expression1 else evaluate expression2.

a=linspace(1,2,2);
b=linspace(1,3,3);
[A,B]=meshgrid(a,b)
fact(A,B,0.1)
function f = fact(m,n,lam)
    if m==n
        f=m.*(n+2)+lam;
    else
        f=0;
    end
end

The above just gives me the matrices A and B and 0 from the else statement. I want it to compare the elements of "m" and "n" and evaluate the "if" part if they are the same. I tried using bsxfun(@eq,m,n) instead of m==n. It gives the same result, 0 from the else part. Below is the output.

Instead, evaluating the following code (no if statement) over the mesh does give me the expected result of the function values over the entire mesh.

a=linspace(1,2,2);
b=linspace(1,3,3);
[A,B]=meshgrid(a,b)
fact(A,B,0.1)
function f = fact(m,n,lam)
        f=m.*(n+2)+lam;
end

gives

A =
   2
   2
   2
B =
   1
   2
   3
ans =
1000    6.1000
1000    8.1000
1000   10.1000

The output I am looking for should look like

1000      0
         8.1000
         0

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Answer 1

Matt J 2020-4-10

3
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/516778-element-wise-conditional-evaluation-of-a-function-over-a-meshgrid#answer_425139

编辑：Matt J 2020-4-10

在 MATLAB Online 中打开

f = (A==B) .* (A.*(B+2)+lam);

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Matt J 2020-4-10

You're welcome, but please Accept-click the answer to indicate that it worked.

James Browne 2020-4-10

That is pretty awesome! Nice work!

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Answer 2

James Browne 2020-4-10

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/516778-element-wise-conditional-evaluation-of-a-function-over-a-meshgrid#answer_425131

在 MATLAB Online 中打开

Hello, I believe that I have developed a solution for you:

a=linspace(1,2,2);
b=linspace(1,3,3);
[A,B] = meshgrid(a,b)
fact(A,B,0.1)
function f = fact(m,n,lam)
f = zeros(size(n,1), size(n,2));
for i = 1:size(n,1)
    for j = 1:size(n,2)
        if m(i,j) == n(i,j)
            f(i,j) = m(i,j)*(n(i,j)+2)+lam;
        else
            f(i,j)=0;
        end
    end
end
end

Hope this at least helps =)

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Adamya Goyal 2020-4-10

Yes. Thank you so much. But, I want to avoid using loops and keep it "vectorized" if possible. Because the mesh I am going to use this for is going to be huge (~10000x10000 or larger).

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