Creating a function 2020a

I am using the 2020a version. I have created a function and saved it as PBTask4p1_f.m

When I put in the following:

function y = PBTask4p1_f(x) 
y=0.8*x.^4-13*x.^2-5*x; 
end

It has this response: >> PBTask4p1_f Not enough input arguments.

Error in PBTask4p1_f

Why isn't it working?

Thank you

[stozaki]

Hello Chloe,

I tried running your function in R2020a.

If you give a value to the argument x, the function printed correctly.

Did you enter a value for the argument x?

function y = PBTask4p1_f(x) 
    y=0.8*x.^4-13*x.^2-5*x; 
end

MATLAB Command Window

>> Y = PBTask4p1_f(1)

Y =

  -17.2000

>> Y = PBTask4p1_f(2)

Y =

  -49.2000

Regards,

stozaki

[Chloe Walton]

Hi Stozaki,

what do you mean give a value to the argument x? i put in exactly what you did above and it still said there was an error. on my notes it says: The function should work for x being a scalar or a vector. they dont tell me to make x= something.

i am meant to create a function file and put this in: (which is what i have done, and saved it as PBTask4p1_f.m)

function y = PBTask4p1_f(x) 
    y=0.8*x.^4-13*x.^2-5*x; 
end

and then put this in a script: i am able to plot the graph on a script but the f(-5) etc doesnt work

y=PBTask4p1_f(-5);
y=PBTask4p1_f(4)
x=-5:0.01:5;
y=PBTask4p1_f(x);
plot(x,y)
xlabel('Input x');
ylabel('Output y');

how did you make your work? it looks the same as mine.

Thank you

[stozaki]

Hi,

Try creating a script like this:

I got the graph displayed correctly.

y=PBTask4p1_f(-5);
y=PBTask4p1_f(4);
x=-5:0.01:5;
y=PBTask4p1_f(x);
plot(x,y)
xlabel('Input x');
ylabel('Output y');

function y = PBTask4p1_f(x) 
    y=0.8*x.^4-13*x.^2-5*x; 
end

Please refer to the following documents : Add Functions to Scripts

stozaki

Answer 1

[Star Strider]

You are not calling it correctly.

Call it (preferably from a script) as:

x = 42;
y = PBTask4p1_f(x)

and:

y =
     2.4662e+006

should then appear in the calling script workspace.