Using fprintf in a for loop to display the output as a set of coordinate points

Hi, I'm having trouble displaying the output of a math problem about critical points of a function as a set of coordinate points. This is my code

syms x y real
y=x*(4-x)^3;dy=diff(y); x_roots=solve(dy,x); y_x_roots=subs(y,x_roots);  
for j=1
    disp('The critical point(s) is/are')
    for k =length(x_roots) & x_roots~=0
        fprintf("(%d,%d)\n",x_roots, y_x_roots)
    end
end

Prints as output:

The critical point(s) is/are
(1,4)
(4,27)
(0,0)

But it should be:

The critical point(s) is/are
(1,27)
(4,0)
(4,0)

Also, the x=4 is multiplicity of 2 or greater. Is there a way I can display it only once?

Thank you.

Answer 1

[Torsten]

syms x y real
y=x*(4-x)^3;dy=diff(y); x_roots=solve(dy,x); y_x_roots=subs(y,x_roots);  
for j=1
    disp('The critical point(s) is/are')
    [~,idx] = unique(x_roots);
    x_roots = x_roots(idx);
    y_x_roots = y_x_roots(idx);
    for k = 1:length(x_roots) 
        if x_roots(k)~=0
          fprintf("(%d,%d)\n",x_roots(k), y_x_roots(k))
        end
    end
end

The critical point(s) is/are

(1,27)
(4,0)

fplot(y,[0 5])

●

[rezheen]

Awesome. Thank you.

Answer 2

[Walter Roberson]

The basic problem is that fprintf() consumes all of each argument before going on to the next argument. Combine that with the fact that you were attempting to print all of the vector at the same time because you did not form the for loop properly.

syms x y real
y=x*(4-x)^3;dy=diff(y); x_roots=solve(dy,x); y_x_roots=subs(y,x_roots);  

    disp('The critical point(s) is/are')

The critical point(s) is/are

    for k = 1:length(x_roots)
        if x_roots(k)~=0
            fprintf("(%d,%d)\n",x_roots(k), y_x_roots(k));
        end
    end

(1,27)
(4,0)
(4,0)

[rezheen]

Thanks. That's a simple, efficient way to do it.