Function Call not working properly

 t = linspace(-10,15,26);

 plot(t, x_general(t))

where x_general is defined as:

 function [x_out] = x_general(x_in)

 if x_in >= -5 & x_in < 5
    x_out = -2 .* abs(x_in) + 10
 elseif x_in > 5 & x_in <= 10
    x_out = 10
 else
    x_out = 0
 end

 end

When I run this, my plot comes up blank. Not sure why this happens?

Answer 1

[Stephen23]

You probably want to be using logical indexing rather than if:

   function y = fun(x)
   y = zeros(size(x));
   idx = x>5 & x<=10; 
   y(idx) = 10;
   idx = x>=-5 & x<5;
   y(idx) = -2 .* abs(x(idx)) + 10
   end

[Daniel Schilling]

What do you mean?

[Stephen23]

"What do you mean?"

The introductory tutorials teach the basic concepts, such as what indexing is, that you will need to know if you want to use MATLAB:

https://www.mathworks.com/help/matlab/getting-started-with-matlab.html

The point is that if does not apply to parts of an array, as you are trying to use it. But you can easily use logical indexing to specify parts of an array, and my answer shows you how.

https://www.mathworks.com/help/matlab/math/array-indexing.html

Answer 2

[Kevin Chng]

t = linspace(-10,15,26);
plot(t, x_general(t))

function [x_out] = x_general(x_in)
  x_out = zeros(1,length(x_in));
  x_out(x_in >= -5 & x_in < 5) = -2 .* abs(x_in(x_in >= -5 & x_in < 5 )) + 10 ;
  x_out(x_in > 5 & x_in <= 10) = 10 ;
end

In yor code, you are not returning the array, you return a single variable which is 0.

[Daniel Schilling]

So how do I return the whole array. I mean I'm essentially calling this as plot(t, x_general(t))

[Kevin Chng]

Create a array first

x_out = zeros(1,length(x_in));

Then assign the number to your array by indexing.

x_out(x_in >= -5 & x_in < 5) = -2 .* abs(x_in(x_in >= -5 & x_in < 5 )) + 10 ;

This code below

x_in >= -5 & x_in < 5

Will give you something like

[ 0 1 0 1 1 1.....]

So that you know which element in your x_in fullfil the condition, and get them out for the calculation.

then Assign the output to some position of element you extracted from x_in.

It is indexing.

[Daniel Schilling]

%Sets the interval for the sinc function

 t = linspace(-2*pi,2*pi);

%Plots sinc using the built in function call

 plot(t,sinc(t))
 hold on

%Plots sinc function with user made function called MySin

 plot(t,MySinc(t));
 hold on

%Defining function "MySinc"

 function [sinc_out] = MySinc(sinc_in)

%Definition of sinc(x)

 if sinc_in ~= 1.0
    sinc_out = sin(sinc_in)./sinc_in;
 else
    sinc_out = 0
 end
 end

So how come this one worked but without indexing perfectly fine but the one I asked the question about didnt? What's the difference?

[Kevin Chng]

Because your condition

sinc_in ~= 0

All is true which is 1.

if any of them is 0, then your condition is false.then you are not allow enter the if.

That's why the code in your question enter else there which is x_out=0