Matlab代碼在三維數組上運行太慢

Question

我正在嘗試向量化以下代碼：

% code before 
% code before 
% a lot of code before we got to the current comment 
% 
% houghMatrix holds some values 
for i=1:n
    for j=1:m
        for k = 1:maximalRadius            
            % get the maximal threshold 
            if houghMatrix(i,j,k) > getMaximalThreshold(k)                           
                lhs = [j i k];

                % verify that the new circle is not listed 
                isCircleExist = verifyCircleExists(circles,lhs,circleCounter);

                % not listed - then we put it in the circles vector 
                if isCircleExist == 0
                    circles(circleCounter,:) = [j i k];                    
                    fprintf('Circle % d: % d, % d, % d \n', circleCounter, j, i, k);
                    circleCounter = circleCounter + 1;                    
                end
            end
        end
    end
end

使用tic tac我得到以下輸出：

>> x = findCircles(ii);
Circle  1:  38,  38,  35 
Circle  2:  89,  51,  34 
Circle  3:  72,  66,  11 
Circle  4:  33,  75,  30 
Circle  5:  90,  81,  31 
Circle  6:  54,  96,  26 

    Elapsed time is 3.111176 seconds.
>> x = findCircles(ii);
Circle  1:  38,  38,  35 
Circle  2:  89,  51,  34 
Circle  3:  72,  66,  11 
Circle  4:  33,  75,  30 
Circle  5:  90,  81,  31 
Circle  6:  54,  96,  26 

    Elapsed time is 3.105642 seconds.
>> x = findCircles(ii);
Circle  1:  38,  38,  35 
Circle  2:  89,  51,  34 
Circle  3:  72,  66,  11 
Circle  4:  33,  75,  30 
Circle  5:  90,  81,  31 
Circle  6:  54,  96,  26 

    Elapsed time is 3.135818 seconds.

意思是平均3.1秒。

我試圖對代碼進行矢量化處理，但是問題是我需要在內部主體中使用索引i,j,k for （對於， for 3rd）。

任何建議如何使代碼矢量化將不勝感激

謝謝

編輯：

% -- function [circleExists] = verifyCircleExists(circles,lhs,total) --
%
%
function [circleExists] = verifyCircleExists(circles,lhs,total)

    MINIMUM_ALLOWED_THRESHOLD = 2;

    circleExists = 0;
    for index = 1:total-1                
        rhs = circles(index,:);
        absExpr = abs(lhs - rhs);
        maxValue = max( absExpr );
        if  maxValue <= MINIMUM_ALLOWED_THRESHOLD + 1
            circleExists = 1;
            break
        end
    end

end

Answer 1

這里是我想做的事情：對於每個有效的三元組，您要檢查是否已經存在附近的三元組，否則，請將其添加到列表中。 如果沒有“鏈接”的可能性，即如果可能的候選體素的每個簇只能容納一個中心，則可以完全矢量化此操作。 在這種情況下，您只需使用：

%# create a vector of thresholds
maximalThreshold = getMaximalThreshold(1:maximalRadius);

%# make it 1-by-1-by-3
maximalThreshold = reshape(maximalThreshold,1,1,[]);

%# create a binary array the size of houghMatrix with 1's 
%# wherever we have a candidate circle center
validClusters = bsxfun(@gt, houghMatrix, maximalThreshold);

%# get the centroids of all valid clusters
stats = regionprops(validClusters,'Centroid');

%# collect centroids, round to get integer pixel values
circles = round(cat(1,stats.Centroid));

或者，如果您要遵循選擇有效圓的方案，則可以從validClusters獲取ijk索引，如下所示：

[potentialCircles(:,1),potentialCircles(:,2), potentialCircles(:,3)]= ...  
       sub2ind(size(houghMatrix),find(validClusters));

nPotentialCircles = size(potentialCircles,1);


for iTest = 2:nPotentialCircles
    absDiff = abs(bsxfun(@minus,potentialCircles(1:iTest-1,:),potentialCircles(iTest,:)));

    if any(absDiff(:) <= MINIMUM_ALLOWED_THRESHOLD + 1)
       %# mask the potential circle
       potentialCircles(iTest,:) = NaN;
    end
end

circles = potentialCircles(isfinite(potentialCircles(:,1)),:);