# How to make a piecewise function and plot it ?

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Luca Amicucci on 29 Sep 2020
Commented: Sudhakar Shinde on 1 Oct 2020
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??
Luca

Sudhakar Shinde on 29 Sep 2020
Instead of using h1, h2,h3 and h4 , you can use h variable for all 4 pieces of code.
then use plot
plot(th2,h);
##### 2 CommentsShowHide 1 older comment
Sudhakar Shinde on 1 Oct 2020
Welcome

R2020b

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