f=@(x) function handle with range + conv

Dear all,

I have these functions with the code that aims to plot the two signals - x(t) and h(t) - alongside their time range then find the convolution of the two signals.

x=@(t) 2.*((-2<=t&&t<=1)+2).^2.*18.*(2<=t&&t<=3).*-9.*((4<=t&&t<=5)-5);
tx=-2:0.01:5;

h=@(t) 3*(0<=t&&t<=2) -6*((4<=t&&t<=4)-3);
th=0:0.01:4;

c=conv(x(tx),h(th));
tc=(tx(1)+th(1)):0.01:(tx(end)+th(end));

figure(1)
subplot(3,1,1); plot(tx,x(tx));
subplot(3,1,2); plot(th,h(th));
subplot(3,1,3); plot(tc,c);

However, I got this error.

Operands to the || and && operators must be convertible to logical scalar values.

Error in @(t)2.*((-2<=t&&t<=1)+2).^2.*18.*(2<=t&&t<=3).*-9.*((4<=t&&t<=5)-5)

I want to use function handle to plot them.

Is there a way to fix this problem?

Thanks in advance for your answers.

Answer 1

[Deepak Gupta]

Hi Aqeel,

Piecewise function is very helpful in writing conditional functions. Check it out:

https://in.mathworks.com/help/symbolic/piecewise.html

As i see multiple errors in your code so providing a piece of code for your reference to solve this problem.

x = @(t) piecewise(t<-2, 0, -2<=t<1, 2*(t+2)^2, 1<=t<3, 18, 3<=t<5, -9*(t-5), t>5, 0);
h = @(t) piecewise(t<0, 0, 0<=t<2, 3*(t+2), 2<=t<4, -6*(t-3), t>4, 0);
tx=-2:0.01:5;
th=0:0.01:4;

xVec = double(subs(x, tx));
hVec = double(subs(h, th));
c = conv(xVec, hVec);
tc = (tx(1)+th(1)):0.01:(tx(end)+th(end));

figure(1)
subplot(3,1,1); plot(tx,xVec);
subplot(3,1,2); plot(th,hVec);
subplot(3,1,3); plot(tc,c);

Cheers.

[Deepak Gupta]

Extra Note: As your function x is not defined at tx = 5 and h at th = 4, hence matlab returns function values NaN at these time instants. To me it seems like a problem with the question. Because of this you don't see convolution plot from -2 to 9 as expected.

[Aqeel Mohamed]

NIce idea, works great!

Though it won't work to those whom MATLAB version is before 2016.

I noticed the extra note, yeah the question has a mistake.

Thank you very much Deepak :)