How can I use the "diff" function instead of a for loop?

Question

Ashfaq Ahmed 2022-1-4

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1621720-how-can-i-use-the-diff-function-instead-of-a-for-loop

评论： Matt J 2022-1-4

Dear altruists,

How can I get the similar result from this few lines of code using the MATLAB built in "diff" function instead of using the for loop?

g = 9.807;
for i=2:size(lon,1)-1
    for j=2:size(lat,2)-1
        dx=double(m_lldist([lon(i+1) lon(i-1)],[lat(j) lat(j)]))*1000;
        dy=double(m_lldist([lon(i) lon(i)],[lat(j+1) lat(j-1)]))*1000;
        f=2*(omega)*sin((lat(j)*(pi/180)));
        u(i,j)=-g/f*(ssh(i,j+1)-ssh(i,j-1))/dy;
        v(i,j)= g/f*(ssh(i+1,j)-ssh(i-1,j))/dx;        
    end
end

the size of the variables: lat, lon, and ssh is the same. (size:71*294)

Any feedback from you will be highly appreciated. Happy new year all!

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Answer 1

Matt J 2022-1-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1621720-how-can-i-use-the-diff-function-instead-of-a-for-loop#answer_867420

编辑：Matt J 2022-1-4

在 MATLAB Online 中打开

[m,n]=size(ssh);
zm=zeros(m,1);
zn=zeros(1,n);
gf=g./(2*omega*sind( lat ) );
Du=diff(ssh(:,2:end),1,2)+diff(ssh(:,1:end-1),1,2); 
   Du=-gf.*[zm,Du,zm];
Dv=diff(ssh(2:end,:),1,1)+diff(ssh(1:end-1,:),1,1);
   Dv=gf.*[zn;Dv;zn];
 [dx,dy]=deal(ones(size(Du)));
   
for i=2:size(lon,1)-1
    for j=2:size(lat,2)-1
        
        dx(i,j)=double(m_lldist([lon(i+1) lon(i-1)],[lat(j) lat(j)]))*1000;
        dy(i,j)=double(m_lldist([lon(i) lon(i)],[lat(j+1) lat(j-1)]))*1000;
    end
end
u=Du./dy;
v=Dv./dx;