How to make a piecewise function and plot it ?

Question

Luca Amicucci 2020-9-29

0
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https://ww2.mathworks.cn/matlabcentral/answers/602026-how-to-make-a-piecewise-function-and-plot-it

评论： Sudhakar Shinde 2020-10-1

采纳的回答： Sudhakar Shinde

在 MATLAB Online 中打开

Hi guys!

I want to write a piecewise function , with 4 case , and so I made this :

H = 2;
w = 209.439509; % 2000 rpm
a = 0;
for i = 1:360
    w2(i,1) = w; % w2 angular velocity (rad/s)
    a2(i,1) = a; % a2 angular acceleration (rad/s^2)
    th2(i,1) = i*pi/180; % radiant
    th2d(i,1) = i; % degree
    
   % first
    if (i) < 90
     h1(i,1) = 0; 
     v1(i,1) = 0; 
     a1(i,1) = 0; 
  
    % second
    
    else if (i) >= 90 && (i) < 180
    
    beta = pi-pi/2;   
       
    h2(i,1) = H/pi*( (pi*(th2(i,1)-pi/2))./beta - 1/2*sin((2*pi*(th2(i,1)-pi/2))./beta)  );
    
    v2(i,1) = (H.*w2(i,1))./(beta) .* ( 1 - cos( (2*pi*(th2(i,1)-pi/2))./beta) ); 
    
    a2(i,1) = ( 2*H*pi.*w2(i,1).^2 ./ beta^2 ).*sin(  (2*pi.*(th2(i,1)-pi/2))./(beta) );
   
       
    % third
    else if  (i) >= 180 && (i) < 240
       
    h3(i,1) = 0; 
    v3(i,1) = 0; 
    a3(i,1) = 0; 
          
    % fourth
    else  (i) >= 240 && (i) < 360
     
    beta2 = -pi/2;
      
    h4(i,1) = H/pi*( (pi*(th2(i,1)-pi*4/3))./beta2 - 1/2*sin((2*pi*(th2(i,1)-pi*4/3))./beta2)  );
    
    v4(i,1) = (H.*w2(i,1))./(beta2) .* ( 1 - cos( (2*pi*(th2(i,1)-pi*4/3))./beta2) ); 
    
    a4(i,1) = ( 2*H*pi.*w2(i,1).^2 ./ beta2^2 ).*sin(  (2*pi.*(th2(i,1)-pi*4/3))./(beta2) );
       
            end
        end
    end
end
figure(1)
plot(th2(1:89),h1);
hold on;
plot(th2(90:179),h2)
hold on;
.....

But it doesn't work because, at the first if statement the vector has the right size (89) , but then at the second if it has the size of the previous one + his correct size ( 89) and so on...

Anyone can help me??

Thanks in advance,

Luca