Subscripted assignment dimension mismatch.

Hi, please i got this error from Matlab. I don't know what the problem

    for j=1:5000
    g=Qom(j)
    Pm=Pm
    r(j)=xcorr([Pm,g],'coeff')
    end

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/signal/ref/xcorr.html#bual1fd-3

"If x is an M × N signal matrix representing N channels in its columns, then xcorr(x) returns a (2*M – 1) × N^2 matrix with the autocorrelations and mutual cross-correlations of the channels of x"

The only time that could give you a scalar output would be if M = 1 and N = 1 -- that is, if you had a scalar input. But unless your Pm is empty, [Pm,g] is going to be a vector, and so the minimum output size you could get would be a 3 x 1 column vector (and might be larger, if Pm is larger.). You cannot store a 3 x 1 column vector into the single location r(j)

[Mustapha hamaoui]

Thanks Walter, but Pm is a Scalar and g is a matrix with 5000 value

[Walter Roberson]

    g=Qom(j)

so g cannot be a matrix. g must be a scalar. So you are using [scalar,scalar] which results in a vector of length 2. So you are using a 1 x 2 input array. M = 1, N = 2. That is going to give you a (2 * M - 1) by (N^2) output, which is (2*1 - 1) by (2^2) which is 1 by 4 output.

... or it would if xcorr were not treating row vector as a special case. It is treating it as a 2 x 1 input, so (2 * 2 - 1) by (1^2) which is 3 x 1, then transposing because the original is a row vector, so the output is 1 x 3.

1 x 3 is not going to fit in a single location r(j)