Question

i am trying this code since last night but i cant understand what this code is doing. actually i am beginner in matlab programming

 load('79.mat')
 trainingData=d79;
 colormap(gray);
 colormap(grey);
 x=reshape(d79(1234,:),28,28);
 y = x(:,28:-1:1); 
 pcolor(y');

Kindly help me in understanding this code. :/

Answer 1

This is pretty simple. Here is a line-by-line explanation:

1. Loads data from a data file
2. Puts the loaded data into a variable named trainingData
3. Sets the colormap for plotting
4. Take the 1234th row of the loaded matrix, convert it into a 28-by-28 matrix, and store it in the variable x. So for example, on a smaller scale, [5 6 7 8] is converted to the matrix [5 7; 6 8] if you want to reshape that matrix to 2-by-2.
5. Reverse the column order of x and put that in y. So the last column becomes the first, second-last becomes second, etc.
6. This is a checkerboard plot of the values contained in y.

Edited to include more detail on lines 5 and 6:

The reshape line assumes that there is a row with number 1234, and that there are 784 (28*28) elements in that row. It takes that row, and makes a 28×28 matrix out of it, by taking the first 28 elements, making them into the first column of the new matrix, then taking the next 28 elements, making them the second column, and so on 26 more times. The final matrix is names x.

For the y line, like I said, it just reverses the columns of x, it puts the last column first, the second-last column second, and so on until the first column of the x is put as the last column of y.