if + for loops vs while loop. Same good different results
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Hello people,
So I am doing an online course. And I am stuck in one of the problems. I have to calculate the period of a pendulum.
This is my code:
function [ T ] = pendulum( L,a0 )
g = 9.8;
a = [];
omega = 0;
theta = a0;
dt = 10^-6;
for time = 0:dt:10
a = g*sin(theta)/L;
omega = omega + a*dt;
theta = theta - omega*dt;
if theta >= 0
T = 4*time;
else
break
end
end
This is the correct answer:
function [ T ] = pendulum( L,a0 )
%PENDULUM Summary of this function goes here
% L positive scalar
% a0 positive scalar less than pi
% alpha = angluar acceleration
% g = acceleration due to gravity
% omega = angular velocity
if L <=0
fprintf('L must be a positive real number')
T=0
return
end
theta=a0;
g=9.8;
omega=0;
deltat=1e-6;
T=0;
while theta>0
T=T+deltat;
alpha=g*sin(theta)/L;
omega=omega+alpha*deltat;
theta=theta-omega*deltat;
end
T=4*T
%formula=T/(2*pi*sqrt(L/g))
end
For L = 2 and a0 = pi/2
my code gives:
3.350336000000000
the correct code gives:
3.350344000012992
So the only difference between the two codes is that I used an if loop inside a for loop and the correct loop used only a while loop. Any ideas what could be the problem?
Thanks
采纳的回答
Work backwards from the end, and look at where the time / T value last changes. They are not the same. The location of the the if and break is important, and/or the logical condition that you use.
Both of these give the same output (to within floating point tolerances):
for time = 0:dt:10
if theta<0
break
end
a = g*sin(theta)/L;
omega = omega + a*dt;
theta = theta - omega*dt;
end
T = 4*time
And
while theta>0
T=T+dt;
alpha=g*sin(theta)/L;
omega=omega+alpha*dt;
theta=theta-omega*dt;
end
T = 4*T
2 个评论
Stephen23
2018-12-14
Orestis Stylianou's "Answer" moved here:
Yes, you are right. Thanks for the help!
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