why the error occur when i use horzcat fuction

the error message

the output from y is matrix [2,3]

then i take only the first element

rr=4;

the output must be rr=[4,2,3]

Answer 1

[Geoff Hayes]

Shehab - are you sure that the y is a 1x2 array like [2,3]? Or is it a 2x1 array like [2,3]'? If the latter, then you are trying to horizontally concatenate a 1x1 scalar with a 2x1 array and so the error makes sesne. From find, this function returns a vector with the same orientation as the input array. And your input at

y = find(a(iu) == matrix(:, i))

suggests that it is a column array/vector since you are comparing against the ith column of matrix. Use the MATLAB debugger to step through the code to validate this.

[Image Analyst]

Before the horzcat line, put this

whos rr
whos y

What do you see in the command window? Do they both have the same number of rows?