Data error at pos 127 after SYEV

[huangchbii]

Hi, I experienced this. After Ssyev, I got Data error at pos 127. I am wondering if this is also because of a singular matrix?

Thanks.

[john]

It's likely that you've hit the limits of single precision; I would recommend trying again in double precision to see if the error persists.

[huangchbii]

Hi,

What do you mean "hit the limits of single precision"? I am using NVIDIA 9400m, can I still use double precision? Dsyev?

In fact, the response of this function some times is strange. Some times I got error at pos 127, some times I got NAN without any error.

My matrix is randomly generated. Do you think if it can be prevented by generating the matrix in a proper way?

[john]

Many eigenvalue problems are numerically sensitive beyond the bounds of single precision. You should probably try dsyev to see if the problem is cured by extra precision. I believe the 9400 can run this, albeit very slowly. CULA will indicate to you if your device does not support double precision by an error code when you call a D routine.