Finding a root in matlab, not compiling - matlab

Question

i have to do an assignment where i have to find the depth of how much the ball is under water depending on the water's density, then i have to plot it. i don't have matlab at home but i'm using octave and for some reason it's not compiling, and it's not saying any errors. here is my code
function my_script()
% weight function
function func = weight(x,p)
func = p *pi* 4- 3 * pi*x ^2 + pi* x ^3;
% make the secant method
function root = secant(func , p, x0, x1, tol, count)
while count ~= 0
y1 = func(x0,p);
y2 = func(x1, p);
k = (x1 - x0)/(y2 - y1);
R = y2 * k;
root = x1 - R;
if abs(func(root,p)) < tol
break;
end
x0 = x1;
x1 = root;
count = count - 1;
end
%create array for depth values
y_val = [];
%input the roots into the array with a loop
for p = 0:0.01:1
t = secant(#weight, p, 0, 1, 0.000001, 1000000);
disp (t);
y_val = [y_val t];
end
% create the x - axis
x_val = 0 : 0.01 : 1;
%plotting the graph
figure;
plot (x_val, y_val)
xlabel('Density');
ylabel('Depth ');
title('Floating Sphere vs Density ');

Answer 1

Another way of creating what you have written is to split it into three different functions.
You'd have the weight function, weight.m,
% weight function
function func = weight(x,p)
func = p *pi* 4- 3 * pi*x ^2 + pi* x ^3;
and the secant method function, secant.m,
% make the secant method
function root = secant(func , p, x0, x1, tol, count)
while count ~= 0
y1 = func(x0,p);
y2 = func(x1, p);
k = (x1 - x0)/(y2 - y1);
R = y2 * k;
root = x1 - R;
if abs(func(root,p)) < tol
break;
end
x0 = x1;
x1 = root;
count = count - 1;
end
%create array for depth values
y_val = [];
%input the roots into the array with a loop
for p = 0:0.01:1
t = secant(#weight, p, 0, 1, 0.000001, 1000000);
disp (t);
y_val = [y_val t];
end
% create the x - axis
x_val = 0 : 0.01 : 1;
%plotting the graph
figure;
plot (x_val, y_val)
xlabel('Density');
ylabel('Depth ');
title('Floating Sphere vs Density ');
Then you'd have my_script():
function my_script()
but it is an empty function, so the output is correct! You have to have all the commands for each function finished before you define the next function.
I have a feeling that you want to take out everything from the end of the while loop onwards from the secant function and put it into the main my_script() function.

Answer 2

Here's your code, Octave style. Observe that I temporarily commented the "disp(t);" statement to avoid a long listing of values. This way, the plot is plotted immediately. Hopefully this helps.
function my_script
%create array for depth values
y_val = [];
%input the roots into the array with a loop
for p = 0:0.01:1
t = secant(#weight, p, 0, 1, 0.000001, 1000000);
%disp (t);
y_val = [y_val t];
endfor
% create the x - axis
x_val = 0 : 0.01 : 1;
%plotting the graph
figure(1)
plot (x_val, y_val)
xlabel('Density');
ylabel('Depth ');
title('Floating Sphere vs Density ');
endfunction
% make the secant method
function root = secant(func , p, x0, x1, tol, count)
while count ~= 0
y1 = func(x0,p);
y2 = func(x1, p);
k = (x1 - x0)/(y2 - y1);
R = y2 * k;
root = x1 - R;
if abs(func(root,p)) < tol
break;
end
x0 = x1;
x1 = root;
count = count - 1;
endwhile
endfunction
% weight function
function func = weight(x,p)
func = p *pi* 4- 3 * pi*x ^2 + pi* x ^3;
endfunction