Prohibit "pcg" writing to command window

Hello,

I got a more cosmetic question concerning matlab function "pcg" https://de.mathworks.com/help/matlab/ref/pcg.html. Is there a way to prevent a command line output from pcg after each (un)successful call? It is annoying and might even slow my program down due to the writing to the command window. Thanks in advance, Daniel

[Geoff Hayes]

Daniel - you may want to post the line of code that you are using to call pcg and an example of the unsuccessful command line output from that call. Do you have a semi-colon at the end of your line of code? Do you observe particular warnings that you wish to suppress (via https://www.mathworks.com/help/matlab/matlab_prog/suppress-warnings.html)? Please clarify.

[Daniel Döhring]

Hi Geoff,

I use the pcg solver for an implicit euler with a linear right-hand side:

for i=1:nts-1
  U(:,i+1)=pcg(Id-(tspan(i+1)-tspan(i))*A, U(:,i));
end

and since nts = number time steps might be very large, I do not want to see every message of a successful pcg solve at the command line. Best, Daniel

[Geoff Hayes]

Daniel - what does the output of a successful call look like?

[Daniel Döhring]

My whole command winwo is full of these messages, is there a way to suppress these messages?

Answer 1

[Geoff Hayes]

Daniel - Wow that is busy. Perhaps try doing

 [x,~,~,iter] = pcg(Id-(tspan(i+1)-tspan(i))*A, U(:,i));
 U(:,i+1) = x;

I noticed that if I just did

 [x] = pcg(Id-(tspan(i+1)-tspan(i))*A, U(:,i));

then I would observe the pcg converged at ... message. But with the other line of code where I have an iteration output parameter, iter, then the message is suppressed.

[Daniel Döhring]

This works out, thanks!

[Josh Meyer]

To clarify for future readers: if you specify the second FLAG output then the function stops printing convergence information to the command window. Instead the value of the FLAG output conveys whether the attempt was successful.

[x,flag] = pcg(...)