If statement in a function

Question

Abdullaziz Errayes 2018-11-23

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/431556-if-statement-in-a-function

编辑： Cris LaPierre 2018-11-23

I have a function that outputs the speeds at times from 0:25 seconds and there are different equations for different times. I would like to know however how to make the function stop at 25 seconds rather than keep going on. As a reference i was trying to use the composite trapezoidal rule to find the distance travelled over time by a camaro for 25 seconds.

format short
clear all
clc
Speed_first=@(t)0.1553567*(t.^6)-2.0416*(t.^5)+9.1837*(t.^4)-14.829*(t.^3)-1.3703*(t.^2)+32.821*t-1.3155;
Speed_second=@(t)0.003980879*(t.^5)-0.2247*(t.^4)+4.8682*(t.^3)-50.442*(t.^2)+254.67*t-430.66;
Speed_third=@(t)-0.073*(t.^2)+6.1802*t+40.423;
time=0:0.01:25;
speed=[];
l=length(time);
for i=1:l
    if (time(i)<5)
        speed(i)=Speed_first(time(i));
    elseif (time(i)<15.4)
        speed(i)=Speed_second(time(i));
    else
        speed(i)=Speed_third(time(i));
    end 
end
subplot(2,1,1)
plot(time,speed)
ylabel('Speed')
xlabel('Time')
title('Time against speed')
N=2;   
Er = 100;     
old_integral = 100; 
Number_sections=[];
Integrals=[];
while Er > 0.00002  
 
    [integral,Distance_vec,time_vec]=inttrapezoidal(N);  
     Number_sections = [Number_sections N]; 
     Integrals = [Integrals integral]; 
     N = N*2;  
    Er=abs(((integral-old_integral)/integral)*100);
    old_integral=integral; 
    fprintf('\n Integral= %g; number of Sections = %g; Relative Error = %f\n',integral,N, Er)
end
subplot(2,1,2)
plot(time_vec, Distance_vec);
title('Cumulative distance by time');
xlabel('Time');
ylabel('Distance travelled');
figure()
semilogx(Number_sections,Integrals); 
title('Distance travelled by number of sections');
xlabel('Number of Sections');
ylabel('Distance travelled');
function [integral,Distance_vec,time_vec] = inttrapezoidal(N)
     a = 0;   
    b = 25;   
    
    h = (b-a)/N;
    Distance_vec(1) = 0.0;
    for m = 2:N
       x_left = a+(m-1)*h;
       x_right = a+m*h;
       f_left = f(x_left);
       f_right = f(x_right);
       Distance_vec(m) = Distance_vec(m-1)+h/2*(f_left+f_right);
       time_vec(m)=x_left;
    end
     integral=Distance_vec(end);
end
  function v = f(time)
  if time<=5
     
        Speed = 0.1553567*(time.^6)-2.0416*(time.^5)+9.1837*(time.^4)-14.829*(time.^3)-1.3703*(time.^2)+32.821*time-1.3155;
  
    elseif time>=5 && time<15.4
        Speed = 0.003980879*(time.^5)-0.2247*(time.^4)+4.8682*(time.^3)-50.442*(time.^2)+254.67*time-430.66;
 
   else
        Speed =-0.073*(time.^2)+6.1802*time+40.423;
    end
    v=Speed*0.47404;
  end
  
 

but as you can see at the end i cant make my function stop at 25 seconds.

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Answer 1

Cris LaPierre 2018-11-23

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/431556-if-statement-in-a-function#answer_348564

编辑：Cris LaPierre 2018-11-23

在 MATLAB Online 中打开

Incorporate the conditions you want into your if statement. To exit a fuction when a specific condition is met, use a return statement.

function v = f(time)
if time<=5
    Speed = 0.1553567*(time.^6)-2.0416*(time.^5)+9.1837*(time.^4)-14.829*(time.^3)-1.3703*(time.^2)+32.821*time-1.3155;
elseif time>=5 && time<15.4
    Speed = 0.003980879*(time.^5)-0.2247*(time.^4)+4.8682*(time.^3)-50.442*(time.^2)+254.67*time-430.66;
elseif time <= 25
    Speed =-0.073*(time.^2)+6.1802*time+40.423;
    
else
    return
end
v=Speed*0.47404;
end