How to plot a piecewise defined function?

Hi

I want to plot a piecewise defined function. My Problem is, that the plot isn't right and I don't find the mistake... would be great, if somebody could help me!

function CubicSpline
clear all; 
clc; 
close all; 

%CatmullRom:
B1=0;
C1=1/2;

x=-2:.01:2;
y1=zeros(size(x)); 

if abs(x)< 1,
    y1=1/6*((12-(9*B1)-(6*C1))*abs(x).^3 +(-18+(12*B1)+(6*C1))*abs(x).^2 + (6-(2*B1))); 
elseif 1 <= abs(x) < 2
     y1 = 1/6*(((-B1-6*C1)*abs(x).^3 + (6*B1+30*C1)*abs(x).^2 + (-12*B1-48*C1)*abs(x)+(8*B1+24*C1)));
else y1 = 0;
end

figure(1);clf; hold on;
plot(x,y1,'r')%,x, y2, 'b', x, y3, 'g'
xlabel('X-Axis')
ylabel('Function values')
grid on;
legend({'CatmullRom: B = 0, C = 1/2'},'Location','EastOutside')

[Azzi Abdelmalek]

Your program is working, what is the expected result?

[Simon]

If B1 = 0, x = 0, abs(x) is 0 and as consequence the y1 value must be 1. When I plot it the y1-value at x=0 is 2

[Jan]

It is a waste of time to remove all loaded function after starting this function by "clear all". This does not even clean the local workspace, because there are no variables declared before.

[Simon]

Ah, thanks. Your're right!

[Simon]

I still have the problem to plot this function. Could anybody help me? Would be nice :-)

Answer 1

[Andrei Bobrov]

B1=0;
C1=1/2;
x0 = -2:.1:2;
x=abs(x0);
y1=zeros(size(x));
t = [x < 1, x >= 1 & x < 2];
y1(t(:,1)) = 1/6*((12-(9*B1)-(6*C1))*x(t(:,1)).^3 +...
                                (-18+(12*B1)+(6*C1))*x(t(:,1)).^2 + (6-(2*B1)));
y1(t(:,2)) = 1/6*(((-B1-6*C1)*x(t(:,2)).^3 +...
            (6*B1+30*C1)*x(t(:,2)).^2 + (-12*B1-48*C1)*x(t(:,2))+(8*B1+24*C1)));

ADD (corrected)

t1 = x0 <= -1;
t2 = x0 > -1 & x0 < 1;
t3 = x0 >= 1;
plot(x0(t1),y1(t1),'r'); hold on
plot(x0(t2),y1(t2),'g');
plot(x0(t3),y1(t3),'k');

[Simon]

Hey, thanks! But now I tried to plot y1, but it doesn't work... how can I plot y1?

plot(x, y1(t(:,:,1,2)),'r')

Sry for the stupid question..

[Andrei Bobrov]

see ADD in my answer

[Simon]

The added Code doesn't work :(

plot(x(t(:,1)),y1(t(:,1)),'r',x(t(:,2)),y1(t(:,2)),'g',x(t(:,3)),(t(:,3)),'r');

This doesn't work, too :(

[Andrei Bobrov]

corrected

[Simon]

Hm... there's only a line with the values x=[-2:.1:2] and y=0

[Simon]

It still doesn'´t work. It could not be that difficult to plot this function. Would be great, if somebody could post the right code and explain it to me :)