MATLAB doesn't plot my function

This is probably a dumb question but when I try to plot this function nothing appears:

format long
y = @(x) - sin(x);
z = @(x) x.^2;
test1 = @(x) y(x)-z(x);
x = fzero(test1,[0 1])
plot(test1)

It also gives my the following error:

error: unary operator '.'' not implemented for 'function handle' operands
error: called from
    __plt__>__plt1__ at line 189 column 8
    __plt__ at line 118 column 18
    plot at line 229 column 10
    ex1 at line 6 column 1

Answer 1

[Alan Stevens]

Try

fplot(test1)

[Pedro Almeida]

Thank you so much!!!

[Askic V]

Another possibility:

y = @(x) - sin(x);
z = @(x) x.^2;
test1 = @(x) -x.^2 - sin(x) %

test1 = function_handle with value:
    @(x)-x.^2-sin(x)

x = fzero(test1, [0 1])

x = 0

t = linspace(-2,2);
f_val = feval(test1, t);
plot(t, f_val)
grid on

[Pedro Almeida]

I'm sorry, but what does this line do exactly? I'm new to MATLAB so appologies if this is too simple.

f_val = feval(test1, t);

[Askic V]

It evaluates the function test1. Please have a look at the documentation:

https://www.mathworks.com/help/matlab/ref/feval.html

Answer 2

[Sam Chak]

Hi @Pedro Almeida

You probably want to plot like this?

y     = @(x) - sin(x);
z     = @(x) x.^2;
fun   = @(x) y(x) - z(x);
fplot(y, [-pi pi]), hold on
fplot(z, [-pi pi]), 
xsol1 = fzero(fun, -1)

xsol1 = -0.8767

xsol2 = fzero(fun, 1)

xsol2 = 6.2882e-26

plot(xsol1, y(xsol1), 'o')
plot(xsol2, y(xsol2), 'p'), hold off
xlabel('x'), grid on, 
legend('sin(x)', 'x^2')

[Askic V]

Great example!