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matlab piece wise function

Asked by JONATHAN KATHUZA on 3 Jun 2019
Latest activity Commented on by darova
on 3 Jun 2019
write a matlab code that plots the following piece wise function f(t) = ( 3t^2 +5 t>0)and f(t)=(-e^t + 5t <0 )

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What have you tried so far?
Edit Rik: copied code from attached file to comment text.
%%ploting a piecewise function
%created by Jonathan kathuza, Promise Kalonga,Christina Mkanyoza,Samuel Mboma
%Fatsani Tamandikani,Wonderful Lijoni Duwa
%02nd June 2019;
a=input('enter starting point \n');
b=input('enter end point \n');
t=a:0.01:b;
y1= -exp(t)+5;
y2=3*(t.^2)+5;
if a<0&&b<0
plot(t,y1)
xlabel('t');
ylabel('y');
elseif a>=0&&b>=0
plot(t,y2)
xlabel('t');
ylabel('y');
elseif a<0&&b>=0
plot(t,y1,'r-',t,y2,'g-')
legend('-exp(t)+5','3*(t.^2)+5;')
else
disp('invalid inputs')
end
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1 Answer

Answer by Rik
on 3 Jun 2019

That is a good idea of solving your problem. There is one thing you're forgetting in your logic: to trim the parts you don't need in the third case. The solution to that is logical indexing, which is a good idea in the first place.
There is some code missing (because I'm not making your homework for you), but these parts should get you where you need to be.
a=-3;b=4;
if a>=b
error('invalid inputs')
end
t=a:0.01:b;
L=___
y=zeros(size(t));
y(~L)= -exp(t(~L))+5;
y(L)=3*(t(L).^2)+5;
But there is an even better solution: you can put your piecewise function in a single anonymous function and let fplot handle your problems. I'm using different conditions and functions as an example here, but you shouldn't have any trouble adapting it to your own problem.
f1=@(t)-exp(t);%function 1
f2=@(t) cos(t*5);%function 2
cond=@(t) sin(t*15)>0;%when this condition is true, set f2 to 0
f=@(t) f1(t).*cond(t) + f2(t).*~cond(t);
fplot(f,[a b])

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