CODEWITHSUNDEEP
matlabvectordetection
MrPitivier
MrPitivier

Reputation: 71

MATLAB: Detection of plus/minus signs in vector

I have a vector, for example:

test = [1 2 -3 -4 -5 -8 1 2 3 -5 -9 -2 3 2 1];

And I would like to detect the changing of plus/minus sign in this vector. I need to detect only the changing of signs. For example, if the sign changed, so print on the command line: 'Change'.

Thank you for your help.

Upvotes: 0

Views: 226

Answers (2)

pysolver
pysolver

Reputation: 525

As @lodestar said, there are many ways to do this. If you are looking for displaying something at the command prompt then you should look at disp. For instance:

>> arrayfun(@(x)disp(['Change at ', num2str(x+1)]),find((test(1:end-1).*test(2:end))<0))

Change at 3
Change at 7
Change at 10
Change at 13

Upvotes: 1

Iodestar
Iodestar

Reputation: 198

There are many possibilities to do this. One of them that doesn't involve for loops is:

test = [1 2 -3 -4 -5 -8 1 2 3 -5 -9 -2 3 2 1]  % Original vector

signs = sign(test);                            % Get vector signs
diff = signs(2:end) - signs(1:end-1);          % Compute difference between
                                               %   successive values
indices = find(diff ~= 0) + 1;                 % Get indices of sign changes

The variable indices then has the values 3, 7, 10 and 13.

Upvotes: 3

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