Disagreement of Matrix dimension

Hello Friends,

I have executed the following codes:

X=[8.3  13.9  12.5  22.2  8.3  11.1  18.1  11.1  6.9  6.9  6.9  19.4  9.7  4.2  5.6  12.5  11.1  6.9  8.3  8.3  13.9  9.7  6.9  6.9  8.3  5.6  12.5  4.2  18.1  11.1  4.2  8.3  12.5  15.3  5.6  6.9  13.9  13.9  18.1  12.5  15.3  29.2  36.1  30.6  22.2  40.3  41.7  52.8  50  52.8  61.1  55.6  72.2  69.4  68.1  68.1  76.4  94.4  77.8  101.4  81.9  73.6  93.1  76.4  48.6  52.8  41.7  44.4  43.1  25  26.4  19.4  25  19.4  16.7  13.9  8.3  15.3  5.6  5.6  5.6  5.6  9.7  6.9  2.8  8.3  9.7  8.3  11.1  12.5  15.3  8.3  13.9  4.2  16.7  5.6  8.3  16.7  4.2  11.1  2.8  8.3  5.6  8.3  4.2  11.1  12.5  8.3  8.3  9.7  13.9  15.3  19.4  20.8  25  23.6  25  25  25  33.3  26.4  23.6  27.8  19.4  22.2  19.4  23.6  26.4  15.3  23.6  15.3  26.4  13.9  9.7  15.3  11.1  11.1  18.1  9.7  16.7  18.1  9.7  11.1  22.2  18.1  13.9  19.4  20.8  18.1  13.9  15.3  19.4  13.9  16.7  20.8  12.5  18.1  15.3  15.3  12.5  8.3  12.5  20.8  15.3  15.3  12.5  13.9  9.7  18.1  8.3  19.4  16.7  12.5  12.5  13.9  6.9  9.7  11.1  16.7  5.6  8.3  11.1  4.2  12.5  2.8  12.5  11.1  8.3  9.7  8.3  8.3  18.1  12.5  11.1  8.3  9.7  6.9  12.5  5.6  8.3  0];

M=2;
N           = length( X );
Z           = ones(N,M) * 1/M;                  % indicators vector
P           = zeros(N,M);                       % probabilities vector for each sample and each model
t           = ones(1,M) * 1/M;                  % distribution of the gaussian models in the samples
u           = linspace(min(X),max(X),M);        % mean vector
sig2        = ones(1,M) * var(X) / sqrt(M);     % variance vector
C           = 1/sqrt(2*pi);                     % just a constant
Ic          = ones(N,1);                        % - enable a row replication by the * operator
Ir          = ones(1,M);                        % - enable a column replication by the * operator
Q           = zeros(N,M);     
thresh      = 1e-3;
step        = N;
last_step   = inf;
iter        = 0;
min_iter    = 10;

when I try to execute the following code,

P = C ./ (Ic*sqrt(sig2)) .* exp( -((X*Ir -Ic*u).^2)./(2*Ic*sig2));

am getting this error:

?? Error using ==> mtimes
Inner matrix dimensions must agree.

The problem I have identified with that code,in particular (X*Ir)is both are matrix but of different sizes, say X = 1R&201C and Ir=1R&1C.

How to handle these different size matrices?

Please help me out.

Also suggest me some alternate codes. Thanks.

kra/-

[Oleg Komarov]

Please format the code with the {} button, will increase the chance of an prompt answer.

[Anandh]

thanks Oleg.

Answer 1

[Andreas Goser]

How to debug this:

1. Format the code in a way Oleg asked for. You help others to help you.

2. If you have a matrix dimension error in one line, split the line into sub-operations in oder to see where it fails, e.g.

P = C ./ (Ic*sqrt(sig2)) .* exp( -((X*Ir -Ic*u).^2)./(2*Ic*sig2)); % fails
exp( -((X*Ir -Ic*u).^2)./(2*Ic*sig2)) % fails
-((X*Ir -Ic*u).^2) % fails
X*Ir % fails - there must be at least one cause

3.

>> whos X Ir
Name      Size             Bytes  Class     Attributes

Ir        1x2                 16  double              
X         1x201             1608  double

-> Now it is clear. 1x201 * 1x2 - > That's not going to work. The question still is, what is it that you need to achieve. Just because I could tell you a working operation, I can't tell you what makes sense.

[Anandh]

Am working to get the maximum likehood estimate from my sample data. The code I have written there is one among them.Can you tell me a correct operation for that 1x201*1x2 matrix?

[Oleg Komarov]

201x1 * 1x2 = 201x2: basics of matrix multiplication, more on wikipedia.

I would suggest to do: (1x2)' * 1x201 = 2x201. Transposing a smaller matrix is more convenient...but it depends also on subsequent operations which at the moment I can't read.

[Andreas Goser]

I would like to refrain from suggesting a certain operation / implementation.

See the examples in the doc here: http://www.mathworks.com/help/techdoc/ref/arithmeticoperators.html

It lists all the ways to multiply two vectors.