Hello,

I have a major problem with a Correlation algorithm I'm trying to implement..

Basically, when I have two small matices:

Matrix 1:

0 1 0 1 1 1

1 1 1 1 1 1

0 1 0 0 0 1

1 1 0 0 0 0

1 1 1 1 1 1

0 0 0 0 0 0

Matrix2:

0 1 0 1 1 1

1 1 1 1 1 1

0 1 0 0 0 1

1 1 0 0 0 0

1 1 1 1 1 1

0 0 0 0 0 0

The result would be: 0.00142383

If I changed Matrix 2:

0 0 0 0 0 0

1 1 1 1 1 1

0 0 0 0 0 0

1 1 1 1 1 1

0 0 0 0 0 0

0 0 0 0 0 0

The result would be: 0.000263672

This is correct and works perfectly.. But I'm working on 2 512x512 matrices and when I try to find the Correlation it produces a number like: 1.64643e-14 which is obviously wrong.. I have tried everything.. Here is the algorithm I was given:

-Find the mean value of both matrices; subtract each element of

the matrices by its mean value

-For the numerator, multiply matrices element by element; take

the sum of the resultant matrix after multiplication

- For the denominator,square each matrix element by element;

take the sum of each squared matrix; multiply the sum; square

the multiplied results

- Divide the numerator by the denominator

The larger the similarity score, the more similar the matrices are

And here is my algorithm:

```
double Matrix::getMean(double* theMatrix)
{
double add = 0;
double mean = 0;
for(int i=0; (i < rows); i++)
{
for(int j=0; (j < columns); j++)
{
add += theMatrix[i*rows+j];
}
}
mean = add/(rows*columns);
return mean;
}
double Matrix::getSum(double *theMatrix)
{
double sum = 0;
for(int i=0; (i < columns); i++)
{
for(int j=0; (j < rows); j++)
{
sum += theMatrix[i*rows+j];
}
}
return sum;
}
double* Matrix::squareMatrix(double* theMatrix)
{
for(int i=0; (i < rows); i++)
{
for(int j=0; (j < columns); j++)
{
const int transformedIndex = i * rows + j;
theMatrix[transformedIndex] = theMatrix[transformedIndex]*theMatrix[transformedIndex];
}
}
return theMatrix;
}
double Matrix::Correlation(double* matrix1, double* matrix2)
{
double Matrix1Mean = getMean(matrix1);
double Matrix2Mean = getMean(matrix2);
double* matrix3 = new double[rows*columns];
for(int i=0; (i < columns); i++)
{
for(int j=0; (j < rows); j++)
{
matrix1[i*rows+j] -= Matrix1Mean;
matrix2[i*rows+j] -= Matrix2Mean;
}
}
for(int i=0; (i < rows); i++)
{
for(int j=0; (j < columns); j++)
{
matrix3[i*rows+j] = matrix1[i*rows+j]*matrix2[i*rows+j];
}
}
//cout << matrix1[20] << endl;
double* squareMatrix1 = squareMatrix(matrix1);
double* squareMatrix2 = squareMatrix(matrix2);
double sum1 = getSum(matrix1);
double sum2 = getSum(matrix2);
double denominator = pow((sum1*sum2),2);
double numerator = getSum(matrix3);
double final = numerator/denominator;
cout << final;
}
```

Does anyone have any ideas? Thanks :)

*Edited
by phorce*: n/a