Plot Error: Vectors should be the same length

So basically guys, please help.

I don't understand, I am writing a script which should plot a graph.

When I use it independently, it works: (here is the script)

x = -10:0.01:10;

plot(x,q1,'g',x,q2,'r'),

axis([-3 3 -3 3])

x = linspace(c(1),c(2),10);

qq1 = -0.34+1.69*(x-0.25).^2;

qq2 = 1.76-0.77*(x-0.71).^2;

xb = [x,x];

yb = [qq1,qq2];

fill(xb,yb,'b')

hold on

xr = [x,x];

yr = [qq2,qq1];

fill(xr,yr,'b')

legend('q1 (x)', 'q2 (x)'),

xlabel('x'), ylabel('q (x)'),

However, the problem arises when I put it together With the rest of the script, sym x;

q1 = -0.34+1.69*(x-0.25).^2;

q2 = 1.76-0.77*(x-0.71).^2;

%find the points of intersection

syms x

equation = -0.34+1.69*(x-0.25).^2 - 1.76+0.77*(x-0.71).^2 == 0;

S = solve(equation,x);

c = double(S)

%find the area of the intersection

f = -0.34+1.69*(x-0.25).^2 - 1.76+0.77*(x-0.71).^2;

z = int(f, c(1), c(2));

w = abs(z);

display('Area: '), disp(double(w));

%plot the graph

x = -10:0.01:10;

plot(x,q1,'g',x,q2,'r'),

axis([-3 3 -3 3])

x = linspace(c(1),c(2),10);

qq1 = -0.34+1.69*(x-0.25).^2;

qq2 = 1.76-0.77*(x-0.71).^2;

xb = [x,x];

yb = [qq1,qq2];

fill(xb,yb,'b')

hold on

xr = [x,x];

yr = [qq2,qq1];

fill(xr,yr,'b')

legend('q1 (x)', 'q2 (x)'),

xlabel('x'), ylabel('q (x)'),

and I run the script and get this error:

Error using plot

Vectors must be the same length.

Error in Matlab_01 (line 21)

plot(x,q1,'g',x,q2,'r'),

Can somebody please help find where I am making the mistake? Thank you beforehand.

[Adam]

Please format code in a Code { } block in future. It makes it so much easier to read. And whilst I am in favour of blank lines around code to break it up I think every other line being blank does not aid readability!

Answer 1

[Adam]

You seem to keep reusing 'x'. I see 3 different places where it is redefined. The final one seems to make it a vector of length 10, whereas q1 is of an unknown length as it appears to be the first line of the script based on whatever x was at the time which might well have been:

x = -10:0.01:10;

You can use the debugger to very easily see these things. Either with a breakpoint on the relevant line you want to stop at or using the 'Stop on errors' option from the Breakpoints menu.

Answer 2

[Star Strider]

Try this:

figure
fplot(q1, [min(x) max(x)], 'g')
hold on
fplot(q2, [min(x) max(x)], 'r')
hold off
axis([-3 3 -3 3])

Use ezplot if you do not have fplot. They should produce the same results here.