MATLAB: Error using +. Matrix dimensions must agree

error matrix dimensionneural network

Hi, I'm trying to create neural network for train my data. But I get error. I though its right but which one should I fix. Here my code
%clc;
close all;
clearvars;
% Multilayer Perceptron (MLP) neural networks.
N = 220; %sum of data
D = 25 ; %dimension
K = 11; %target
h = 500; %sum of neuron
load datatrain1.mat 
Train1= cell2mat(Train);
load classtrain1.mat
CTrain1 = cell2mat(TTrain);
b1 = randn(1,h);%bias from input to hidden
W1 = randn(D,h);%weight from input to hidden
b2 = randn(1,K);%bias from hidden to output
W2 = randn(h,K);%weight from hidden to output
%feedfoward
for efoch = 1 : 1000
    H = Train1*W1+b1;
    Y = H*W2+b2;
end
I get error in variable H, like this Error using +. Matrix dimensions must agree.
Any help for fix my code will must appreciated. Thanks

Best Answer

The error message is very clear, you're trying to add two matrices of different size, which is never possible. Since b1 is a 1xh vector, Train1*W1 must be a 1xh vector, and since W1 is a Dxh matrix, Train1 must be a 1xD vector for the product to be 1xh.
Therefore, your train1 is not 1xD. There is nothing we can do about that. Either use a train1 matrix that is 1xD or change your D to reflect the size of train1.
Note that it is never a good idea to hardcode the size of matrices. It is always safer to ask matlab for the actually size:
D = size(train1, 2);
would ensure it always match train1. Of course, train1 must only have one row.
edit: got confused between D and h but see comment below.
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