adding constraints with if loop

Question

Bibek 2012-2-3

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/27998-adding-constraints-with-if-loop

采纳的回答： Walter Roberson

a1=1:.3:5.2;

b1=3:.2:5.8;

c1=2:.3:6.2;

for k=1:15

composite=[a1(:,k) b1(:,k) c1(:,k)];

origin=[1.3 1.1 1.5];

d(:,k)=sqrt(sum((composite-origin).^2));% 1*15 vector

end

But now in 'composite' I want to exclude those all points which have a1 less than or equal to 1.5, b1 greater than or equal to 5 and c1 less than or equal to 2. So now my d vector will be 1*6 instead of 1*15. How can I get this result with combination of for and if loop.

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Bibek 2012-2-4

You are right. I mean 'if conditional'. Thanks!

Walter Roberson 2012-2-4

'S'ok. I'm just trying to prevent the phrase from spreading as several people started using it.

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Answer 1

Walter Roberson 2012-2-4

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在 MATLAB Online 中打开

And if it must be done with "for" and "if" then,

a1=1:.3:5.2;
b1=3:.2:5.8;
c1=2:.3:6.2;
origin=[1.3 1.1 1.5];
numv = 0;
d = [];
for k=1:15
  composite=[a1(:,k) b1(:,k) c1(:,k)];
  if composite(1) <= 1.5 || composite(2) >= 5 || composite(3) <= 2;
    continue;
  end
  numv = numv + 1;
  d(:,numv)=sqrt(sum((composite-origin).^2));
end

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Bibek 2012-2-4

You used if+continue+end. I guessed that your code continue the calculation of d when if statements do not hold good and ends calculation of d when if conditions are true. Am I right? How can I do it other way, e.g. find d only when a1 is greater than 1.5, less than 5; b1 less than or equal to 5;c1 greater than or equal to 2 and less than 5.8. Otherwise when these if statements do not apply end my calculation.

can it also be done with while+break and for+break. Thanks!

Walter Roberson 2012-2-4

if composite(1) >= 1.5 & composite(1) < 5 & composite(2) <= 5 & composite(3) >= 2 & composite(3) < 5.8

numv = numv + 1;

d(:,numv)=sqrt(sum((composite-origin).^2));

end

This is a different way of writing the same control: select what you do want rather than rejecting what you do not want.

When you say "end my calculation", if you mean for the entire loop over "k", then before just before the "end" of the "if", add

else

break

But take note that this will result in no work being done, as a1(1) is out of the desired range. So probably you just want to do what I have written here, do not calculate the result if the values are out of range for this k.

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Answer 2

Walter Roberson 2012-2-3

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/27998-adding-constraints-with-if-loop#answer_36273

在 MATLAB Online 中打开

a1=1:.3:5.2;
b1=3:.2:5.8;
c1=2:.3:6.2;
composite=[a1(:), b1(:) c1(:)];
Lidx_a = a1 <= 1.5;
Lidx_b = b1 >= 5;
Lidx_c = c1 <= 2;
composite((Lidx_a | Lidx_b | Lidx_c),:) = [];
nrow = size(compisite,1);
origin=[1.3 1.1 1.5];
d = sqrt( sum( (composite-repmat(origin,nrow,1)).^2, 2) );