Splitting a massive matrix into blocks - c++

Question

I have a problem. I'm working on a task that tries to find a matrix (vector) inside another matrix(vector) and the size of the matrices are:
Massive Matrix: 1024x768
Small Matrix: 36x49
Basically, my theory was to split the massive matrix into blocks that were the size of the small matrix thus meaning I was able to just see whether the small matrix exists in which block and then output the block. However, it just will not split equally but I need a way to determine if the small matrix does actually exist in the massive matrix.
As an example, I'll use test data:
M1 =
0 1 0 0
1 1 1 1
0 0 0 0
1 0 1 1
M2 =
0 1
1 1
And then I would split the matrices into blocks of 2x2 and then check that way. This is simple as I'm only working with a small matrix AND the matrix can be split equally, whereas the problem above is a lot more complex to understand and figure out.
In essence, I need to be able to split the (1024x768) into block sizes of (36x49) so then I can do the check to determine where that particular matrix is. I have been working with this algorithm:
// Assume:
// matrix1ColSize = 768
// matrix2ColSize = 49
const int ROW_BOUNDS = matrix1.size() - matrix2.size();
const int COL_BOUNDS = matrix1ColSize - matrix2ColSize;
bool found = false;
for(int i=0; (i < ROW_BOUNDS); i++)
{
bool matchFound = false;
for(int j=0; (j < COL_BOUNDS); j++) {
// logic here
}
cout << endl;
}
Could anyone offer any advice please? This is really annoying me now :(!

Answer 1

Two matrices are the same if all their elements are the same. So the following pseudo-code compares the small matrix with a block in the large matrix:
Initialize result to "true"
For each position in the small matrix
Read the value from the large matrix; call it x1
Read the value from the small matrix; call it x2
If x1 is not equal to x2, set result to "false"
(Optional) If x1 is not equal to x2, stop looking at other positions
Here, use the result
This logic is going to be inside your 2 nested loops, so you will have 4 nested loops there! If you fear of getting confused, put the implementation inside a function. If you want to use 4 nested loops, good luck.
In c++:
bool is_equal = true;
for (int y = 0; y < 49; ++y)
{
for (int x = 0; x < 36; ++x)
{
if (matrix1.at(j + x, i + y) != matrix2.at(x, y))
{
is_equal = false;
goto DONE; // optional
}
}
}
DONE:;
Edit: this code assumes using a custom class for matrices; after looking again at your code i realize that you probably use a vector of vectors (std::vector<std::vector<int>>), so use matrix2[y][x] instead of matrix2.at(x, y).