cov in R2009b vs. R2010a

I used the cov function in R2009b and in R2010a and it returned different results.

I am aware of the fact that there are multiple functions named cov in Matlab, depending on your toolboxes; both functions are in the directory matlab/datafun

The revision date on both functions is $Revision: 5.16.4.8 $ $Date: 2009/03/16 22:17:40 $.

What could be producing this discrepancy?

edit: R2009b is on a Mac (OS X 10.5.8); R2010a is on a PC (7).

[Laura Proctor]

Could you post the code that you ran as well as the results?

Answer 1

[Walter Roberson]

This is not entirely unexpected. The BLAS toolboxes are optimized for specific processors, so differences in processors can result in differences in calculations. Likewise, differences in the JIT of the different versions of MATLAB can result in the same code producing different results.

If the differences are small relative to the results, the situation is probably normal.

Answer 2

[D]

Sorry, it seems to be a question of precision. I subtracted the two matrices for comparison, but I missed the factor of 1.0e-15 that multiplied the resulting matrix.

[Sean de Wolski]

"Time for another cup of coffee" moment.