Error using gmres. Too many output arguments.

I am pretty sure about this code that it is working I copied it from a textbook. But when I run it I get the error

"Error using gmres. Too many output arguments." I did all I could but I couldn't able to fix the problem, I think the reason being that I am not strong in matlab coding. Help needed.

clear
m=200;A=2*eye(m)+0.5*randn(m)/sqrt(m);b=ones(m,1);
[x,flag,relres,iter,resvec]=gmres(A,b);
figure(1)
plot(eig(A),'o');
hold on;
x=(1.5:0.001:2.5);
plot(x,sqrt(0.25-(x-2).^2),'r',x,-sqrt(0.25-(x-2).^2),'r');
legend('eigenvalues of A','(x-2)^2+y^2=1/4')
figure(2)
n=1:length(resvec);
semilogy(n,resvec);
hold on;
semilogy(n,4.^(-n),'r');
legend('||r^n||/||b||','4^{-n}');
hold off

Answer 1

[Hmm!]

Yes. The resolution is that I had another file in the path folder with gmres so removing that file to a different folder did the magic. Thanks ot @Christine Tobler for the insight.

Answer 2

[Yongjian Feng]

It is working, at least for 2021a. Which version are you using please?

When matlab outputs an error, it normally tells you which line as well. Does it say line 3?

[Hmm!]

I am using MATLAB Version: 9.7.0.1261785 (R2019b) Update 3. It didn't tell me the line but when I run the code line by line, the error begins at

[x,flag,relres,iter,resvec]=gmres(A,b);

[Christine Tobler]

Perhaps you have another file called gmres.m on the path, which overrides the standard one?

Try

which -all gmres

this should list any additional gmres.m that MATLAB might try to call here.