topic Problem about using FGMRES in IntelĀ® oneAPI Math Kernel Library
https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Problem-about-using-FGMRES/m-p/976168#M17109
<P>I write a code in C using mkl FGMRES to solve a Ax=b linear system. I follow the example code given in mkl handbook here: http://sepwww.stanford.edu/sep/claudio/Research/Prst_ExpRefl/ShtPSPI/intel/mkl/10.0.3.020/examples/solver/source/dcsrilu0_exampl1.c, which use ILU0 as the preconditioner. The structure of the code is almost the same as the example code so I don't put it here. Now I met a problem. For some problems, my code can solve the problem successfully; but sometimes it can not. </P>
<P>For example, today it happens like this: I put A, b and initial guess solution into the code, when it run after calling dfgmres function, depending on the value of RCI_request parameter, it will do different operations (for example if RCI_request = 0, then we get the answer; if RCI_request = 1, we should do what what). This example will keep repeat RCI_request = 1 and RCI_request = 3, and the while loop in the code will not stop and I can not get the answer. My guess is that the matrix A doesn't have a good property (for example condition number is too large,etc) and the solver can not deal with it. But I am not sure about this. My question is in what condition the RCI_request can repeat between 1 and 3? How can I make sure this is because of the bad property of the input matrix A? If this is ture, does it mean FGMRES can not solve this problem?</P>
<P>Another question is about the preconditioner. In the example code, it used ilu0 as the preconditioner. If the solver can not deal with one problem well, if I change to a different preconditioner (like LU), will it help or not? </P>
<P>Also, which parameter, the number of rows N in the matrix, or the number of non-zeros M in matrix A will determine the scalibility of this FGMERES solver?</P>
<P>Thanks.</P>
<P>C.J.X</P>Fri, 31 May 2013 07:04:06 GMTC_J_X_2013-05-31T07:04:06ZProblem about using FGMRES
https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Problem-about-using-FGMRES/m-p/976168#M17109
<P>I write a code in C using mkl FGMRES to solve a Ax=b linear system. I follow the example code given in mkl handbook here: http://sepwww.stanford.edu/sep/claudio/Research/Prst_ExpRefl/ShtPSPI/intel/mkl/10.0.3.020/examples/solver/source/dcsrilu0_exampl1.c, which use ILU0 as the preconditioner. The structure of the code is almost the same as the example code so I don't put it here. Now I met a problem. For some problems, my code can solve the problem successfully; but sometimes it can not. </P>
<P>For example, today it happens like this: I put A, b and initial guess solution into the code, when it run after calling dfgmres function, depending on the value of RCI_request parameter, it will do different operations (for example if RCI_request = 0, then we get the answer; if RCI_request = 1, we should do what what). This example will keep repeat RCI_request = 1 and RCI_request = 3, and the while loop in the code will not stop and I can not get the answer. My guess is that the matrix A doesn't have a good property (for example condition number is too large,etc) and the solver can not deal with it. But I am not sure about this. My question is in what condition the RCI_request can repeat between 1 and 3? How can I make sure this is because of the bad property of the input matrix A? If this is ture, does it mean FGMRES can not solve this problem?</P>
<P>Another question is about the preconditioner. In the example code, it used ilu0 as the preconditioner. If the solver can not deal with one problem well, if I change to a different preconditioner (like LU), will it help or not? </P>
<P>Also, which parameter, the number of rows N in the matrix, or the number of non-zeros M in matrix A will determine the scalibility of this FGMERES solver?</P>
<P>Thanks.</P>
<P>C.J.X</P>Fri, 31 May 2013 07:04:06 GMThttps://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Problem-about-using-FGMRES/m-p/976168#M17109C_J_X_2013-05-31T07:04:06ZCan anyone help?
https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Problem-about-using-FGMRES/m-p/976169#M17110
<P>Can anyone help?</P>
<P>About this fgmres solver, I have another question. Now my input matrix A is a M-matrix, which has all the diagonal elements to be 1 and all off diagonal elements are negtive and much smaller than 1. A is pretty sparse matrix. For this kind of matrix, it should be a good matrix (small condition number). But in my solver sometimes it will not get converged. Size of A is about 100K by 100K, non-zeros is about 10 million. I want to check the condition number of A but it means I will write another code to realize this and it self will be time consuming...</P>
<P>Any suggestion for my problem? Thanks!</P>
<P>C.J.</P>Mon, 03 Jun 2013 19:46:13 GMThttps://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Problem-about-using-FGMRES/m-p/976169#M17110C_J_X_2013-06-03T19:46:13ZPlease refer the FGMRES
https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Problem-about-using-FGMRES/m-p/976170#M17111
<P>Please refer the FGMRES detail in the MKL manual located at</P>
<P><A href="http://software.intel.com/sites/products/documentation/hpc/mkl/mklman/GUID-56F0C6ED-0A49-48C4-AF7B-33C3851A39CA.htm">http://software.intel.com/sites/products/documentation/hpc/mkl/mklman/GUID-56F0C6ED-0A49-48C4-AF7B-33C3851A39CA.htm</A></P>Wed, 05 Jun 2013 07:03:59 GMThttps://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Problem-about-using-FGMRES/m-p/976170#M17111VipinKumar_E_Intel2013-06-05T07:03:59Z