Calculating cpu usage when running matlab program.

16 次查看（过去 30 天）
jonathan douglas-smith
评论： Walter Roberson 2016-1-25
Hi there,
Would this code be correct in giving me the cpu usage?
close all; clear;
tstart = tic;
initime = cputime;
prompt = ('Please enter time step');
result = input(prompt);
tstep = result;
%define known variables
g = 9.81; c = 12.5; m = 70;
%define analytic time vector
t = 0 : tstep : 10;
%get analytic velocity using equation from lectures
v_analytic = (g*m/c)*(1-exp(-c*t/m));
%set up plot and plot analytic velocity
figure(1); hold on; grid on; box on;
plot(t,v_analytic,'b*-')
title('parachutist');
xlabel('time (s)');
ylabel('velocity (m/s)');
%do numerical calculations here using a 'for' loop
v1 = 0;
N = length(t);
v(1)=0;
for i = 2 : N;
v(i) = v(i-1) + (g-c*v(i-1)/m)*(tstep);
end
%numerical results
plot(t,v,'ro-')
legend('analytical','numerical')
%do error calculations at 5s here
Eabs = abs(v_analytic(5) - v(5));
Erel = Eabs/v_analytic(5);
fintime = cputime;
telapsed = toc(tstart);
display(tstep, 'tsize');
display(Eabs,'Absolute error');
display(Erel,'Relative error');
display((fintime -initime)/telapsed,'CPU usage (%):');
I think this is correct. I want to establish the cpu usage under different input conditions (stepsizes) as if the stepsize is smaller then more calculations are made by the program.
  1 个评论
Walter Roberson
Walter Roberson 2016-1-25
You cannot bold formatted code. If you want to bring attention to particular code lines, add a comment to them.

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Walter Roberson
Walter Roberson 2016-1-25
It is recommended that you use timeit() . If you have an older MATLAB that does not have that built in, you can find it in the File Exchange.
  3 个评论
显示 1更早的评论
jonathan douglas-smith
jonathan douglas-smith 2016-1-25
编辑：jonathan douglas-smith 2016-1-25
This way I am using the cputime function to record cputime before and after the for loop and then using the timeit() function to record the real time used by the program to complete the for loop?
Then I calculate the cpu usage using: fintime -initime)/telapsed.
Does this seem right?
Walter Roberson
Walter Roberson 2016-1-25
There is an example at http://www.mathworks.com/help/matlab/ref/timeit.html . You put the code to be timed in a function or function handle and timeit() the handle.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by