Calling in a function inside a for loop and storing each answer separetly

Hello, this is my code so far. My function outputs the number of iterations needed to solve a system, and I want to use this script to output the number of iterations but with varying a parameter as shown:

A = [-10 4 1 0; 4 -10 0 1; 1 0 -10 4; 0 1 4 -10];
B = [-200;-80;-300;-180];
n = 4;
x = [0;0;0;0];
imax = 1000;
es = 1e-6;
w= 1.2;

for w=0.1: 0.1: 1.9
    engr3202_gsrelax(A,B,n,x,imax,es, w);
end

I keep getting large numbers of iterations so i'm not sure if the code is just adding them all together, but i basically want 19 outputs separately so i can plot a graph with it.

Thanks a lot!

Answer 1

[Walter Roberson]

A = [-10 4 1 0; 4 -10 0 1; 1 0 -10 4; 0 1 4 -10];
B = [-200;-80;-300;-180];
n = 4;
x = [0;0;0;0];
imax = 1000;
es = 1e-6;
wvals = 0.1: 0.1: 1.9;
for widx = 1 : length(wvals)
    w = wvals(widx);
    gs(widx,:) = engr3202_gsrelax(A,B,n,x,imax,es, w);
end
plot(wvals, gs)

[Nadine Nassar]

gs(widx,:) = engr3202_gsrelax(A,B,n,x,imax,es, w);

Could you explain why you put a colon here?

Thank you

[Walter Roberson]

We do not know the size of your output for each call. Using the colon allows for the possibility that you return a vector for each call.

[Nadine Nassar]

Okay, this really helped. Thanks a lot!

Answer 2

[Bhaskar R]

You have not provided the output varibles of the function engr3202_gsrelax(A,B,n,x,imax,es, w);

Make output variables in the calling, I assume only one variable here, say output and intialize with length of w

A = [-10 4 1 0; 4 -10 0 1; 1 0 -10 4; 0 1 4 -10];
B = [-200;-80;-300;-180];
n = 4;
x = [0;0;0;0];
imax = 1000;
es = 1e-6;
w= 1.2;
w=0.1: 0.1: 1.9;
output = zeros(1, length(w));
for iw=0.1: 0.1: 1.9
    output(:, iw) = engr3202_gsrelax(A,B,n,x,imax,es, iw);
end

You can get the data in the variable output for all your loop iterations(19 in our case)

[Walter Roberson]

Now, this will not work. You are trying to use the non-integer iw as an index into output(). And

length(w=0.1: 0.1: 1.9)

is not valid syntax.

[Bhaskar R]

Yes, I corrected now. Thanks

[Nadine Nassar]

output(:, iw) = engr3202_gsrelax(A,B,n,x,imax,es, iw);

Could you explain the colon here?

Thank you

[Nadine Nassar]

Never mind, I understand now.

Thanks a lot for your help!