How to create a graph time vs value n

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Emilia
Emilia on 3 Dec 2020
Commented: Emilia on 3 Dec 2020
Hello,
I have a function that we enter a value n. Next I designed a matrix here and it measures time (tic,toc) until vector returns result.
Now I want to produce a graph for 4<=n<=50 vs time, How can this created?
Thanks for the helpers :)
function [A,VectorOut,B]= pp(n)
tic
f=4*ones(1,n^2);
m=diag(f);
x = zeros(1,n^2);
x_new = x;
j=0;
while j~=n^2
[m(j+1,j+2)]=-1;
[m(j+1,j+4)]=-1;
[m(j+2,j+1)]=-1;
[m(j+4,j+1)]=-1;
j=j+1 ;
end
t=m(1:n^2,1:n^2);
v=zeros(1,n^2);
v(1)=1;
v(n^2)=1;
A=t;
B=v';
for i = 1:n^2
x_new(i) = (B(i) - sum(A(i,1:i-1).*x_new(1:i-1)) - sum(A(i,i+1:n).*x(i+1:n)))/A(i,i);
end
VectorOut=x_new'
toc
end

Answers (2)

Ameer Hamza
Ameer Hamza on 3 Dec 2020
Edited: Ameer Hamza on 3 Dec 2020
I think it might be better if you move the tic ... toc lines outside the function. For example, remove these lines and then run the following code
n = 4:50;
ts = zeros(size(n));
for i = 1:numel(n)
tic
[A,VectorOut,B]= pp(n(i));
ts(i) = toc;
end
plot(n, ts)
Alternatively, you will need to return the value of 't' too. For example,
function [A,VectorOut,B,t]= pp(n)
tic
f=4*ones(1,n^2);
.. ..
.. ..
.. ..
.. ..
.. ..
VectorOut=x_new'
t = toc
end
and then run the code
n = 4:50;
ts = zeros(size(n));
for i = 1:numel(n)
[A,VectorOut,B,ts(i)]= pp(n(i));
end
plot(n, ts)

Deepak Gupta
Deepak Gupta on 3 Dec 2020
Edited: Deepak Gupta on 3 Dec 2020
Hi Emilia,
Placed of toc in the function will just display the elapsed time there instead you need to return the elapsed time from this function, to the script where you will be called this function. i.e. in your function you can write.
totalTime = toc;
And then return it.
In your script you need to save these times with respect to n values. i.e.
n = 4:50;
totalTime = zeros(1, size(n));
for n
[~, ~, ~, nTime] = pp(n);
totalTime(n-3) = nTime;
end
Now you can plot time vs n.
plot(totalTime, n)
Hope this helps,
Cheers,
Deepak

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