Error using piecewise function

Hello,

I am trying to create this piecewise function but there is an error: 'Incorrect number or types of inputs or outputs for function 'piecewise'.

Error in Q2 (line 7)

x1 = piecewise(ABSt<=1, 1-ABSt,0,0);'

this is the code:

t = linspace(-5,5,1001);

ABSt = abs(t)

x1 = piecewise(ABSt<=1, 1-ABSt,0,0);

I am trying to creat x1 = 1-abs(t) while abs(t) is smaller or equal to 1, otherwise x1=0

is anyone knows what is wrong and how to fix it?

thank you!

Answer 1

[Torsten]

"piecewise" works on symbolic arguments.

Define

t = linspace(-5,5,1001);
x1 = (1-abs(t)).*(abs(t)<=1);
plot(t,x1)

instead.

[Engi]

Thank you, it worked.

Just to understand the logic behind it, (I am pretty new in Matlab) - why shall we not write 'picewise' before (1-abs(t)).*(abs(t)<=1);?

and why is the .* makes it work as we wanted?

[Torsten]

As I wrote, you can define piecewise functions for symbolic inputs:

syms t
f = piecewise(abs(t)<=1,1-abs(t),0)

f = 

fplot(f)

but this doesn't work for numerical inputs for t.

The .* makes it work because you must multiply the numerical vector (1-abs(t)) with the logical vector (abs(t)<=1) elementwise.

The product as written means: multiply the element 1-abs(t(i)) with 1 (for true) if abs(t(i))<=1, else with 0 (for false). The result is a vector x1 that is 1-abs(t(i)) at position i if abs(t(i)) <=1 and 0 else.

[Engi]

Alright, thank you for your help.