Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters. ERROR in plotting graph

clear all
close all
clc
tol=input ('Enter TOLERANCE number:') ;
n=input('Enter ITERATION number:');
n=100; 
f=@(x) (x+1-2*sin(pi*x));
a=0; 
b=0.5; 
if f(a) * f(b)>0
    warning('ít is not applicable:')
    
elseif f(a)==0
    fprintf('The root is %d', a)
elseif f(b)==0
    fprintf('The root is %d', b)
end
pre=0;
for i=1:n
    c=(a+b)/2;
    if f(c)==0
        fprintf('The root is: %d\n', c)
    elseif f(c)*f(b)<0
        a=c;
    elseif f(c)*f(a)<0 
        b=c;
    end
    if abs(c-pre)<=tol
        break;
    end
    pre=c;
end
fprintf('The root is %g with the %.3d tolerance',c,tol)
plot (f=@(x), f(XR_1), 'pre')

Answer 1

[Cris LaPierre]

Your plot syntax is wrong. You cannot define a variable (f) inside your plot command. Use the documentation to identify a valid syntax.

The variable XR_1 is not defined in your code, either.

I see you have defined pre as a variable, but are passing it in as a character array to the plot command in what should be the linespec input.

Since you are only plotting a single point, you will want to include a marker style in your linespec. Perhaps try replacing your plot command with this.

plot(c, f(c),'ro')

[Jim Wilson Owusu]

Thanks for your explanation and solution. sorry for late response.