https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Schur-with-Sparse-PARDISO-Complex-matrix/m-p/1080779#M22797 <P>I am using PARDISO to compute a Schur complement &nbsp;matrix. I am testing with real matrix meaning that I am using complex numbers with 0 imaginary parts. When the matrix size is small, the imaginary part of the result is zero but when the size increases, I get a small imaginary part. For example, for a 110000X11000 matrix and a Schur matrix size of about 100x100, the imaginary part is about 1e-6 to 1e-5 smaller than the real part. I would assume the imaginary part should be always 0. I know that numeric error can exist but I would think it is impossible to have anything than 0 by combining zero numbers.Also, a 1e-6 accuracy in double precision does not look that good. &nbsp;Am I wrong? If it is needed I can provide an example. I will need to make a simplified code for that.</P> <P>Thanks,</P> <P>Marc&nbsp;</P> Fri, 27 Jan 2017 19:19:53 GMT marcsolal 2017-01-27T19:19:53Z https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Schur-with-Sparse-PARDISO-Complex-matrix/m-p/1080779#M22797 <P>I am using PARDISO to compute a Schur complement &nbsp;matrix. I am testing with real matrix meaning that I am using complex numbers with 0 imaginary parts. When the matrix size is small, the imaginary part of the result is zero but when the size increases, I get a small imaginary part. For example, for a 110000X11000 matrix and a Schur matrix size of about 100x100, the imaginary part is about 1e-6 to 1e-5 smaller than the real part. I would assume the imaginary part should be always 0. I know that numeric error can exist but I would think it is impossible to have anything than 0 by combining zero numbers.Also, a 1e-6 accuracy in double precision does not look that good. &nbsp;Am I wrong? If it is needed I can provide an example. I will need to make a simplified code for that.</P> <P>Thanks,</P> <P>Marc&nbsp;</P> Fri, 27 Jan 2017 19:19:53 GMT https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Schur-with-Sparse-PARDISO-Complex-matrix/m-p/1080779#M22797 marcsolal 2017-01-27T19:19:53Z https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Schur-with-Sparse-PARDISO-Complex-matrix/m-p/1080780#M22798 <P>I am sorry. This was a mistake. I do not know how to remove this post.</P> <P>Marc</P> Sat, 28 Jan 2017 00:39:49 GMT https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Schur-with-Sparse-PARDISO-Complex-matrix/m-p/1080780#M22798 marcsolal 2017-01-28T00:39:49Z