Operands to the || and && operators must be convertible to logical scalar values. Error in logspace (line 23) if d2 == pi || d2 == single(pi)

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zaid 2014-2-25

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回答： zaid 2014-2-27

i have a vector of current and vector of voltage , i want to get logarithmic samples from both vectors instead of equally spaces. i try current=[...........] voltage=[...........] logspace(current,voltage) it will give me error.

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Wayne King 2014-2-25

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please tell us what voltage is. For example what does

>>whos voltage

return

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Answer 1

Iain 2014-2-27

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Assuming that logspace is something you didn't write and you can't change the if statement:

 for i = 1:1666
  logarithmic_space(i) = logspace(current(i),voltage(i)) 
 end

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Answer 2

Jos (10584) 2014-2-25

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Apparantly, one of the expressions d2 == .. is not a logical scalar. My first guess would be that d2 is not a scalar, but an array with more than 1 element. Can you insert a

disp(size(d2))

just before the if statement?

Then, what would you like to do when there are more elements in d2. Compare them all to pi? ALL and ANY may help you out here:

help all
help any

In addition, comparing floating points using == is tricky. Take a look here:

d2 = 0.1+0.2+0.3
if d2==0.6
   disp('d2 equals 0.6') 
else
  disp('d2 does NOT equal 0.6')
end

Not quite what you would expected. The solution to compare two floating point values, is to use a tolerance:

if abs(valueOne - valueTwo) < TOL
 ...
end

where you can define a tolerance.

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zaid 2014-2-27

thank you, Wayne King and jos, but my main problem is how can i get logarithmic space from my data that i got it from an experiment . i have current vector of 1666 samples and voltage of same number of samples.so size(current)= 1666 1 and current = 1666 1 i want to get data samples as logarithmic space of current vs voltage.

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