How to generate and calculate with empty values of matrix-elements

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Emerson De Souza
Emerson De Souza 2011-8-28
PROBLEM:
I want to use logical functions to perform calculations between
matrices and don't know how to generate an empty value NaN.
EXAMPLE:
I use the two matrices below and if the conditions are not satisfied,
the output should be empty:
clear all;
close all;
m=rand(10,5);
n=rand(10,5);
T = zeros(size(m)); % Make another array to fill up...
for i = 1:numel(m)
if m(i)>.5 && n(i)>.5
T(i) = m(i+1)+n(i+1);
else
T(i) = 'NaN';
end
end
However, I obtain the following error:
??? In an assignment A(I) = B, the number of elements in B and
I must be the same.
I hope someone know the correction of this mistake
Thank you in advance
Emerson
  1 个评论
Oleg Komarov
Oleg Komarov 2011-8-28
Please format the code as indicated here: http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

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采纳的回答

Paulo Silva
Paulo Silva 2011-8-28
T(i) = 'NaN';
is wrong, your arrays have numeric values but you are trying to put one string in the array, you can't mix numeric values with strings on arrays, do this instead:
T(i) = NaN;
See this simple example:
a=[1 2;3 4];a(1)='NaN'; %error because of what I told you
a=[1 2;3 4];a(1)=NaN; %No error
  1 个评论
Emerson De Souza
Emerson De Souza 2011-8-28
Thank you Paulo,
I learned it. On the other hand, I obtain the problem with the assigning to T(i) (see comments from Oleg).
I'm trying to reformulate the problem.
Thank you for your help
Emerson

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更多回答（1 个）

Oleg Komarov
Oleg Komarov 2011-8-28
You can write directly:
NaN
instead of
'NaN'
but my suggestion would be to preallocate NaNs directly and delete the else part:
T = NaN(size(m))
The other problem is that you are assigning to T(i) the next values in m and n, but if i = 50 then the index will exceed the matrix dimensions.
So, what do you want to accomplish here? (you can also avoid the loop)
EDIT replaced & with |:
m = rand(10,5);
n = rand(10,5);
T = [m(2:end,:) + n(2:end,:); NaN(1,size(m,2))];
T(m(1:end-1,:) <= .5 | n(1:end-1,:) <= .5) = NaN;
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Emerson De Souza
Emerson De Souza 2011-8-30
I don't know what is wrong, but it is not working consistently for all elements. Sometimes is correct, but not always.
Could you please have a look on it?
Thanks
Emerson
Oleg Komarov
Oleg Komarov 2011-8-30
You have to be careful when checking m and n, if their first element are both bigger than .5 then the first element of T is the sum of the SECOND elements of m and n.
After correcting for the | I do get consistent results. Try to replace in my example:
m = rand(3);
n = rand(3);
You'll be able to visualize and compare more easily.

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