Hi every body, I write this code and I want to find a new Sol and Soll in iteration 1000 or more but the problem that the answer go to Nan?!

clc
clear all
Npoiv=25;
Npoip=9;
Sol=zeros(75,1);
Soll=zeros(9,1);

deltt=0.01;
Reyn=1;
vis=1;
ntime=500;
SysM=rand(75,75);
SysD=rand(75,75);
SysF=rand(75,75);
SysL=rand(9,75);
SysLT=SysL';
SysK=rand(9,9);

for i=1:Npoiv
    Sol(i)=0.000034;
    Sol(i+Npoiv)=0;
    Sol(i+2*Npoiv)=0.000033;
end
for i=1:Npoip
    Soll(i)=0.0988;
end
for i=1:ntime
    p=Soll;   
    SysM1=SysM*Sol;
    SysD1=SysD*Sol;
    SysL1=SysLT*Soll;
    SysF1=SysF*Sol;
    SysT=(deltt/2*Reyn)*(SysL1-(vis*SysD1)-(Reyn*SysF1))+SysM1;
    a1=inv(SysM)*SysT;
    SysD2=SysD*a1;
    SysF2=SysF*a1;
    SysT1=(deltt/Reyn)*(SysL1-(vis*SysD2)-(Reyn*SysF2))+SysM1;
    a2=inv(SysM)*SysT1;
    SysL2=SysL*a2;
    SysK1=SysK*Soll;
    SysN1=-(2*Reyn/deltt).*SysL2+SysK1;
    Soll=inv(SysK)*SysN1;
    
    SysM2=SysM*a2;
    SysL3=SysLT*(Soll-p);
    SysN=(deltt/2*Reyn)*SysL3+SysM2;
    Sol=inv(SysM)*SysN;
    ntime=i;
    
end

[Jan]

Most likely not the cause of the problem, but a general hint: Do not use inv() explicitly. Replace

a1=inv(SysM)*SysT
% by
a1 = SysM \ SysT

Why do you set the final value of the loop ntime to the current loop index in each iteration?

ntime=i;  % ???

Answer 1

[Jan]

Use the debugger to find the iteration, which causes the NaNs:

dbstop if naninf

Then Matlab stops, when the first NaN occurs. Now you can check the current values.

[Anas Haboobi]

Thank you very much %Jan