Resampling matrices in a loop using interp2

Question

Dinuka Kankanige 2022-12-3

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1869977-resampling-matrices-in-a-loop-using-interp2

评论： Star Strider 2022-12-12

I'm trying to resample 200 matrices of 300*500 size to 30*50 using interp2. My objective is to load each resampled matrix into workspace after running the loop. In the code given here, it indicates there's an issue with how I use interp2 within the for-loop. Could someone please help me resolve this? Or any better approaches than this are also welcome.

-Thank you-

%filepath to directory where data is located

filepath='C:\Users\Task 1\';

%root part of filename (part that doesn't change each time)

filestem='VOD_Au_0dot1degree_';

for i=1:200

%loading files into a struct

A(i)=load(strcat(filepath,filestem,num2str(i),'.mat'));

%resampling

%new matrix column & row size

nc=50;nr=30;

%current matrix column & row size

c=500;r=300;

[C,R]=meshgrid(1:(c-1)/(nc-1):c,1:(r-1)/(nr-1):r);

downscaled_vod(i)=interp2(double(A(i).vod_monthly),C,R);

figure(i)=imagesc(downscaled_vod(i));

end

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Answer 1

Star Strider 2022-12-3

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https://ww2.mathworks.cn/matlabcentral/answers/1869977-resampling-matrices-in-a-loop-using-interp2#answer_1119062

在 MATLAB Online 中打开

I am not certain what hte problem is, since the error messagd is not part of the provided information.

I suspect the problem is in saving a matrix to a scalar, defined by:

downscaled_vod(i)

That can be solved by saving it to a cell array element:

downscaled_vod{i}

The same sort of problem could be due to the ‘double(A(i).vod_monthly)’ reference, although without more information, I cannot determine that.

A = exp(-((1:300).'-150).^2/3000) * exp(-((1:500)-250).^2/5000); % Create Matrix To Be Interpolated

figure

surf(A, 'EdgeColor','none')

colormap(turbo)

title('Original')

i = 1;

nc=50;

nr=30;

c=500;

r=300;

rv = linspace(1,r,nr);

cv = linspace(1,c,nc);

[C,R] = meshgrid(cv, rv);

downscaled.vod{i} = interp2(A, C, R);

figure

surf(downscaled.vod{i})

colormap(turbo)

title('Downscaled')

Using linspace to create the interpolation vectors is likely more efficien than the current code.

Also, put all these:

nc=50;

nr=30;

c=500;

r=300;

rv = linspace(1,r,nr);

cv = linspace(1,c,nc);

[C,R] = meshgrid(cv, rv);

before the loop, because they don't change in loop iterations. There is no need to create them in each iteration.

.

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Dinuka Kankanige 2022-12-12

Thank you. This is helpful.

Star Strider 2022-12-12

As always, my pleasure!

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Answer 2

Matt J 2022-12-3

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1869977-resampling-matrices-in-a-loop-using-interp2#answer_1119107

移动：Matt J 2022-12-3

在 MATLAB Online 中打开

It is wasteful here to use meshgrid. Also, you should hoist C and R out of the the loop since they don't change with i:

    %resampling
    %new matrix column & row size
    nc=50;nr=30;
    %current matrix column & row size
    c=500;r=300;
    [C,R]=deal(1:(c-1)/(nc-1):c,1:(r-1)/(nr-1):r);
   
for i=1:200
    %loading files into a struct
    A(i)=load(strcat(filepath,filestem,num2str(i),'.mat'));
   
    downscaled_vod{i}=interp2(double(A(i).vod_monthly),C,R);
 
    figure(i)=imagesc(downscaled_vod{i});
end