Calculation for pattern correlation

Hi,
I use the built-in function pattern_cor to calculate the pattern correlation
coefficient of my result. I find that the r is strange and different from
the result I compute myself. Here is the script that I use:

r_x = pattern_cor(X,O,1.0,1) ; r_x = 0.9998
r_y = pattern_cor(Y,O,1.0,1) ; r_y= 0.99996

Avg_X = avg(X)
Avg_Y = avg(Y)
Avg_O = avg(O)

Sum_X = 0.0
Sum_y = 0.0
Sum_dev_X = 0.0
Sum_dev_Y = 0.0
Sum_dev_O = 0.0

do i=0, 67
do j=0, 67

Sum_x = Sum_x + (X(i,j) - Avg_X)*(O(i,j) - Avg_O)
Sum_y = Sum_y + (Y(i,j) - Avg_Y)*(O(i,j) - Avg_O)
Sum_dev_X = Sum_dev_X + (X(i,j) - Avg_X)*(X(i,j) - Avg_X)
Sum_dev_Y = Sum_dev_Y +(Y(i,j) - Avg_Y)*(Y(i,j) - Avg_Y)
Sum_dev_O = Sum_dev_O +(O(i,j) - Avg_O)*(O(i,j) - Avg_O)

end do
end do

R_x = Sum_x/(sqrt(Sum_dev_X)*sqrt(Sum_dev_O)) ; R_x = 0.70

R_y = Sum_y/(sqrt(Sum_dev_Y)*sqrt(Sum_dev_O)) ; R_y = 0.98

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Received on Tue Oct 18 22:06:09 2011