If Condition with array of elements

Question

Uday padidela 2014-9-26

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https://ww2.mathworks.cn/matlabcentral/answers/156302-if-condition-with-array-of-elements

回答： David Young 2014-9-28

采纳的回答： Guillaume

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Can anyone help me how to write this condition

if (ra >= 1.12246*sigma)

    uw=0.0; 
end

Here my ra is any array of elements like and the condition should satisfy each element of an array.

So how should i write it

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Answer 1

Guillaume 2014-9-26

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编辑：Guillaume 2014-9-26

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Use all (or any if you just want some elements to statisfy the condition)

if all(ra >= 1.12246*sigma)
  %...
 end

Note, this assume ra is a vector and sigma is scalar. If ra is a matrix:

if all(ra(:) >= 1.12246*sigma)
  %...
end

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Guillaume 2014-9-28

You'll have to be clearer than 'it's not working'.

What are the values of ra and sigma_, and what result do you expect?

Uday padidela 2014-9-28

编辑：Uday padidela 2014-9-28

I have given the details of my code in the thread If condition is not working

My ra values are from 0 to 8.7345 with interval of 0.1066.

And my sigma have 3 values 32, 16.15 and 0.3.

I have used this condition in my potential.

My potential should decay and die off to zero on long run of my ra, but its not so.

Thank you

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Answer 2

Stephen23 2014-9-26

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编辑：Stephen23 2014-9-26

Actually you don't need to do anything. In MATLAB, the if function already is defined to be satisfied IFF every element of the conditional array is non-zero.

The documentation states this clearly "An evaluated expression is true when the result is nonempty and contains all nonzero elements (logical or real numeric). Otherwise, the expression is false."

So you example will calculate the code within the if, only if all of (ra >= 1.12246*sigma) are true.

If you only need some of them to be true, then you will need to use an any.

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Uday padidela 2014-9-28

Thank you for the answer.

But the condition is working.

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Answer 3

David Young 2014-9-28

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You should try to state more clearly what is not working. Give an example set of initial values, say what you expect the result to be, and say what result you actually get. Without this, it's really hard to help you.

All the same, here's a guess. Maybe you need:

uw(ra >= 1.12246*sigma) = 0.0;

This applies the test to each element of ra and sets the corresponding element of uw to zero if the element of ra passes the test.